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Bkockway,  M.D.,  Ass't  Demonstrator 
of  Anatomy,  College  of  Physicians  and 
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PRACTICEOF MEDICINE, including  Ner- 
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sary, Department  of  Surgery  and  Genito- 
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LEA  BROTHERS  &  CO..  PUBLISHERS,  PHILADELPHIA. 


Th?  Students*  Quiz  Scries. 


PHYSIOLOGY. 


A  MANUAL  FOR  STUDENTS  AND  PRACTITIONEUS. 


BY 

FREDERICK  A.   MANNING,  M.  D., 

Attending  Surgeon,  Manhattan  Hospital,  New  York. 


SERIES  EDITED  BY 

BERN   B.  GALLAUDET,  M.D, 

Demonstrator  of  Anatomy,  College  of  Physicians  and  Surgeons,  New  York;  Visiting 
Surgeon  Bellevue  Hospital,  New  York. 


PHILADELPHIA : 
LEA  BROTHERS  &  CO. 


Entered  according  to  Act  of  Congress,  in  the  year  1892,  by 

LEA  BROTHERS  &  CO., 

In  the  Oflace  of  the  Librarian  of  Congress,  at  Washington.    All  rights  reserved. 


Westcott  4  Thomson,  William  J.  Dornan, 

Stereotypers  and  Electrolypers,  Philada.  Printer,  Philada. 


PREFACE. 


The  present  book  is  a  brief  summary  of  the  salient  features 
of  Human  Physiology.  It  is  not  intended  to  compete  with  nor 
to  take  the  place  of  the  more  elaborate  text-books.  The  idea 
has  been  to  present  the  subject  in  such  a  manner  as  to  fix  in 
the  memory  facts  already  learned  in  less  limited  treatises. 

There  is  no  claim  of  originality  for  this  book.  It  is  practi- 
cally and  of  necessity  an  abstract  of  standard  works,  and  princi- 
pally of  those  of  Dalton,  Foster,  and  Kirke.  The  arrangement 
has  in  a  general  way,  been  made  to  conform  with  that  of  the 
last-named  authority.  The  cuts  are  many  of  them  from  Dal  ton's 
Physiology.  Doubtful  questions  have  often  been  referred  to 
Foster,  whose  Text-booh  of  Physiology  is  the  reference-book  of 
a  large  proportion  of  the  schools.  Some  of  the  histological 
descriptions  are  derived  from  Prudden's  Practical  Normal  His- 
tology. 

New  York. 


CONTENTS, 


PAGE 

General  Considerations  and  Proximate  Principles 17 

The  Blood 22 

Circulation  of  the  Blood 27 

Kespiration 36 

Digestion 42 

Absorption 59 

Animal  Heat 62 

Secretion:   The  Mammary  Glands;   The  Skhi ;  The  Kidneys  and 

the  Urine;  The  Vascular  Glands 64 

Muscle 82 

Nutrition 89 

Nervous  System  :  The  Nerves ;  Sympathetic  System ;  Spinal  Cord ; 

The  Medulla  Oblongata;  The  Pons  Varolii  and  Crura  Cerebri; 

The  Cerebrum ;  The  Cerebellum  ;  The  Cranial  Nerves 93 

The  Senses  :  Touch ;  Taste ;  Smell ;  Hearing ;  Sight 145 

Embryology  :  Eeproductiou ;  Development ;  Parturition 173 


APPENDIX. 

Table  op  the  Development  of  an  Eiwbryo 205 

Chemical  Tests  used  Commonly  in  Physiological  Analysis  .    .    205 

Metric  System 207 

5 


PHYSIOLOGY. 


GENERAL  CONSIDERATIONS  AND  PROXIMATE 
PRINCIPLES. 

Define  human  physiology. 

Human  Physiology  is  that  branch  of  biology  which  refers  to 
the  functions  and  properties  of  the  organs  in  the  living  human 
body. 

In  entering  upon  the  study  of  the  functions  of  organs  it  becomes 
desirable  to  understand  something  of  the  nature  of  the  fundamental 
elements  of  living  tissue  which  we  call  cells. 

What  are  cells? 

Cells  may  be  described  as  nucleated  masses  of  protoplasm  of 
microscopic  size,  usually  possessing  limiting  membranes  known 
as  cell-walls,  and  capable  of  passing  through  the  changes  which 
are  characteristic  of  life  and  death.  Some  cells  do  not  possess 
a  nucleus,  but  this  is  quite  exceptional.  More  commonly  each 
cell  has  a  nucleus  or  more  than  one,  and  in  many  instances  there 
is  a  nucleolus  within  the  body  of  the  nucleus. 

What  is  protoplasm? 

Protoplasm  is  an  unstable  albuminoid  substance  of  more  or  less 
gelatinous  nature.     Its  reactions  are  those  of  albumin  (coagulation 
:  by  heat  and  mineral  acids),  and  its  chemical  composition  is  of  vary- 
ing proportions  of  the  elements  C,  H,  N,  0,  S.     Protoplasm  is  living 
albumin  or  proteid. 

Illustrate  the  life  of  the  cells  by  the  amoeba. 

The  characteristic  changes  through  which  cells  pass  are  well 
illustrated  by  the  amoeba  :  {a)  The" power  of  spontaneous  move- 
ment, in .  which  a  small  portion  of  the  cell  is  first  advanced,  and 
2— Phy.  17 


18  GENERAL  CONSIDERATIONS. 

then  the  whole  cell  seems  to  flow  to  and  into  its  branch,  (i) 
Motion  in  response  to  various  phj-sical  and  chemical  stimuli. 
(c)  The  power  of  taking  food,  absorbing  portions  and  rejecting 
the  rest.  ((^)  Reproduction  of  its  kind.  This  is  accomplished  by 
splitting  of  the  cell  into  two,  each  with  it.s  own  nucleus  and  life- 
history,  (e)  Death,  in  which  the  constituent  elements  undergo 
chemical  changes.  All  cells  follow  more  or  less  clo.sely  this  cycle 
of  changes  by  which  we  differentiate  living  matter  from  unorgan- 
ized substances. 

Name  some  of  the  kinds  of  cells  found  in  man. 
Epithelial,  connective-tissue,  blood-,  and  nerve-cells. 

What  is  epithelium  ? 

The  name  '•  epithelium  "  is  given  t(t  the  cells  which  cover  the  skin, 
mucous  and  serous  membranes  of  the  body,  and  also  enter  into  the 
formation  of  the  glands.  Its  varieties  are — (1)  Simple,  a  layer 
of  flat  (s(iuanious),  cubical,  (spheroidal),  or  cylindrical  (columnar) 
cells,  as  in  the  serous  and  mucous  surfaces ;  (2)  sfra/ijicil,  when  it 
occurs  in  layers,  as  in  the  skin  ;  (3)  transldoiKil,  wliere  it  has  the 
characteristics  of  both  in  situations  where  the  other  two  forms 
approach  one  another,  as  in  the  ureters.  (4)  In  the  glands  are 
found  finicfiaiud  n/ls,  winch  partake  of  the  character  of  the  epi- 
thelium of  the  surface.  They  arc  arranged  in  groups  about  the 
ducts.  Such  cells  are  often  known  as  secreting  or  glandular  epi- 
thelial cells. 

What  is  ciliated  epithelium  ? 

The  simple  epithelium  posses.se.s  hair-like  proces.ses  in  certain 
locations,  and  this  is  known  as  riliafrd  ipithcUnm.  The  hairs  are 
endowed  with  motion,  and  wave  in  such  manner  as  to  throw  for- 
ward small  particles  wliidi  f;i]]  upon  them. 

Name  the  chief  uses  of  epithelium. 

Protection,  as  skin,  serous  surfaces;  motion,  ciliated  epithelium 
of  air-passages  and  Fallopian  tubes  ;  secretion,  in  glands — p.  g. 
gastric  juice;  .sen.sation,  in  the  cones  of  the  retina,  olfactory  cells 
of  nose,  etc. 

What  is  endothelium  ? 

It  is  a  simple  form  of  squamous  or  scale-like,  flat  epithelial  cells 
which  line  the  serous  membranes  and  the  blood-vessels.     The  cells 


PROXIMATE  PRINCIPLES.  19 

are  very  delicate,  and  are  not  stratified.  They  are  of  various  forms, 
usually  irregularly  polygonal,  and  are  joined  at  tte  edges  so  as  to 
form  a  sort  of  mosaic. 

What  are  connective  tissues? 

They  are  the  structures  which  form  the  frame  and  supports  of 
the  body  and  of  the  organs  of  the  body.  The  ligaments,  tendons, 
fascige,  cartilage,  and  bones  are  examples  of  them.  The  fibrous 
connective-tissue  cells  are  found  in  all  organs  in  greater  or  less 
amount.  In  the  organs  whose  use  is  the  support  of  the  body  or 
one  of  its  members  these  cells  predominate.  In  other  organs  the 
fibrous  cells  serve  to  hold  in  place  the  functional  cells  and  to 
maintain  the  shape  of  the  organs. 

What  are  the  proximate  principles  of  the  hody  ? 

They  are  the  substances  entering  into  the  composition  of  the 
body,  and  are  inorganic  and  organic. 

What  are  the  inorganic  elements  ? 

Chemically,  C,  H,  0,  N  make  up  a  very  large  portion  of  the 
body-weight,  water  alone  (H2O)  forming  about  three-fourths  of 
the  total.  Besides  these,  sodium,  potassium,  lime,  and  magnesium, 
in  chemical  combinations  with  sulphur,  phosphorus,  chlorine,  and 
carbon  (sulphates,  phosphates,  chlorides,  and  carbonates),_  are 
found  in  considerable  amounts,  and  less  abundantly  iron,  silica, 
and  fluorine.  Occasionally  minute  quantities  of  some  of  the  other 
metallic  elements— arsenic,  lead,  copper,  and  manganese— are  found. 

How  are  the  organic  proximate  principles  classified  ? 

(1)  Nitrogenous,  and  (2)  non-nitrogenous. 

(1)  The  former  take  the  principal  part  in  the  formation  of  solid 
constituents  of  the  body,  and  occur  in  all  the  body  tissues  and 
fluids.  They  make  up  the  protoplasm  of  cells  and  essential  in- 
gredients of  the  fluids,  both  circulatory  and  excretory.  Chemi- 
cally, they  are  compounds  of  C,  H,  0,  N,  sometimes  with  sulphur 
or  phosphorus. 

(2)  The  latter  (non-nitrogenous)  class  of  bodies  are  made  up  of 
the  fats  and  carbohydrates. 

What  is  the  reaction  of  the  fluids  of  the  hody  ? 

Alkaline,  with  only  four  notable  exceptions.  These  are — gas- 
tric juice,  perspiration,  vaginal  mucus,  and  acid  urine. 


20 


PROXIMATE  PRINCIPLES. 


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22  THE   BLOOD. 

THE  BLOOD. 
What  is  blood  ? 

Blood,  while  circulating  in  the  body,  is  a  somewhat  viscid,  opaque 
fluid,  of  a  red  color ;  this  color  varies  in  different  parts  of  the  body 
from  a  brilliant  scarlet  to  a  deep  purple  or  nearly  black  color.  It 
consists  of  a  nearly  colorless  liquid  (plasma  or  liquor  sanguinis),  in 
which  swim  the  blood-corpuscles  or  globules. 

What  are  the  physical  characteristics  of  blood  ? 

It  has  a  specific  gravity  at  60°  F.  (15°  C.)  of  1055  (1045-1062)  ; 
a  faintly  alkaline  (potassium  phosphate)  reaction ;  temperature 
about  100°  F.  (37.8°  C.) ;  a  salty  taste ;  and  an  odor  which  is 
characteristic,  and  often  peculiar  to  the  animal  from  which  it  is 
taken.  When  taken  from  the  body  it  tends  to  form  a  clot  or 
coagulum  (crassamentum). 

What  is  the  quantity  of  the  blood  ? 

About  one-twelfth  of  the  body-weight,  and  is  distributed  as  fol- 
lows in  round  numbers : 

About  one-fourth  in  heart,  lungs,  and  large  vessels ; 

"  "  in  liver ; 

"  "  in  muscles ; 

"  "  in  other  organs. 

Describe  the  formation  of  a  clot. 

If  blood  be  drawn  into  a  shallow  vessel  and  exposed  to  the  air,  it 
will  become  semisolid  at  the.  surface  in  two  or  three  minutes.  This 
jelly-like  condition  will  extend  to  the  sides  of  the  vessel,  and  then 
throughout  the  entire  mass,  so  that  if  the  vessel  be  inverted  the 
blood  will  not  flow  at  the  end  of  ten  or  fifteen  minutes.  Then 
drops  of  pale  fluid  (serum)  begin  to  appear  at  the  surface,  and 
these  unite  to  form  an  amount  of  fluid  sufficient  in  an  hour  to  float 
the  clot,  which  meanwhile  is  contracting  from  the  sides  of  the 
vessel.  The  serum  continues  to  exude  and  the  clot  to  contract  for 
twenty-four  to  thirty-six  hours.  The  color  of  the  clot  remains  red, 
while  the  serum  has  a  pale  straw  color. 

Why  does  blood  clot? 

Clotting  is  due  to  the  formation  of  a  substance  called  fibrin^ 
which  appears  as  a  mesh  of  fine  fibrils  and  soon  entangles  the 
corpuscles.     This  mesh  of  fibrin  contracts  and  squeezes  out  the 


THE   BLOOD. 


23 


watery  elements  of  the  blood  to  form  serum,  and  holds  the  solid 
components,  as  shown  by  diagram  as  follows : 


Blood. 


Plasma. 


Corpuscles. 


Serum. 


I 
Fibrin. 


Clot. 


I 
Clotted  blood. 

What  is  the  source  of  the  fibrin  ? 

Largely,  if  not  entirely,  from  the  plasma.  A  substance  known 
s  j)h(!<t)u'ite  is  obtained  from  plasma  by  saturation  with  salt,  Avith- 
c  \t  which  there  is  no  formation  of  fibrin  :  and  this  substance  redis- 
so-ved  readily  clots  and  forms  fibrin.  Plasmine  may  be  imitated 
by  uniting  solutions  o^  fibrinogen  and  paragJohuJin,  obtained  from 
plasma.  A  third  element  is  considered  probable,  and  this  is  known 
as  the  fibrin  ferment:  it  is  probably  derived  from  the  colorless 
blood-corpuscles.  There  is  some  reason  for  the  belief  that  para- 
globulin  is  not  an  active  factor  in  forming  fibrin,  but  that  it  may 
unite  with  and  render  inert  some  substance  (unknown)  which  pre- 
vents the  formation  of  fibrin  in  the  conditions  of  life. 

Mention  some  conditions  which  affect  the  coagulation  of  blood. 

Retard  or  prevent. 

Greater  heat  or  extreme  cold  retard 
or  entirely  check. 

Contact  with  living  tissues,  espe- 
cially blood-vessels. 

Absence  of  air  retards.  After  death 
by  asphyxia  blood  remains  fluid  ;  also 
when  air  is  withheld  from  drawn 
blood,  as  by  film  of  oil. 

Agitation  of  vessel  retards. 

More  then  twice  the  bulk  of  water. 

Addition  of  viscid  substances — e.  7. 
glycerin,  syrup. 

Addition  of  neutral  salts,  about  2 
per  cent,  solution. 

Digestive  ferments. 

Strong  acids  or  alkalies. 


Hasten. 
Moderate  warmth,  100°-120°  F. 

Contact  with  foreign  matters. 

Access  of  air. 


Eest. 

Addition  of  moderate  amounts  of 
water. 


24  THE   BLOOD. 

Why  does  not  blood  clot  in  the  living  vessels? 

The  reason  is  not  clearly  understood,  but  it  is  supposed  tbat  the 
living  blood-vessels  exert  a  restraining  influence  upon  the  formation 
of  the  fibrin  ferment.  The  formation  of  a  clot  may  occur  in  a  vessel 
after  injury  of  the  lining  by  ligation,  by  the  introduction  of  a  for- 
eign substance,  or  by  disease  of  the  vessel.  This  fact  is  made 
apparent  in  the  ligation  of  vessels,  in  the  treatment  of  aneurism, 
and  in  the  formation  of  emboli. 

What  are  the  principal  forms  of  blood-corpuscles  ? 

The  red  or  colored,  and  white  or  colorless.  They  make  up 
nearly  half  (40-45  per  cent.)  of  the  total  weight  of  fluid  blood. 
The  proportion  of  the  red  to  the  white  is  about  500  to  1. 

Describe  the  red  blood-corpuscles. 

Human  colored  blood-corpuscles  are  circular,  biconcave  disks 
with  rounded  edges ;  in  diameter  they  are  about  -^jq-q  in.,  in  thick- 
ness about  Y2-Jo"¥  ^^-  -'-^  water  they  swell  and  become  flat  or 
convex.  When  seen  singly  they  appear  yellow,  but  their  color  is 
red  when  seen  in  groups.  Microscopic  examination  shows  that 
they  have  no  nucleus  and  no  limiting  membrane  (which  defects 
preclude  the  name  "cell");  but  they  have  an  elastic  framework 
or  stroma,  which  retains  an  individuality  for  each  corpuscle,  and 
allows  changes  of  shape  to  adapt  them  for  capillary  circulation, 
and  brings  them  back  to  the  original  form  after  such  distortion. 

Why  are  they  red? 

Because  the  stroma  of  each  corpuscle  is  infiltrated  with  a  red 
coloring  matter,  hsemoglobm. 

Mention  some  other  peculiarities  of  red  cells. 

(1)  Blood-corpuscles  (sp.  gr.  1088)  are  somewhat  heavier  than 
plasma  (sp.  gr.  1030),  and  therefore  tend  to  sink  when  drawn  in 
a  vessel.  In  blood  that  coagulates  slowly  the  corpuscles  have  an 
opportunity  to  do  this,  and  the  result  is  a  formation  of  fibrin  at 
the  surface  of  the  clot.  This  surface  is  of  a  light  yellowish  color, 
and  is  known  as  the  "  bufi"y  coat." 

(2)  The  red  corpuscles  in  the  process  of  clot-formation  form  in 
rolls  or  columns  like  piles  of  coins,  the  corpuscles  adhering  to  one 
another  at  the  edges,  and  the  columns  so  formed  adhere  to  one 
another  by  their  ends,  so  as  to  make  clusters. 


THE    BLOOD.  25 

Are  the  red  corpuscles  the  same  in  man  as  in  the  animals? 

In  inauiiuals  the  geiiuial  eliaracttT  ol'  tlie  curpu.scle.s  is  tlie  .same 
as  in  man,  but  the  size  of  the  corpuscles  varies  in  different  animals. 
In  reptiles,  fishes,  and  birds  the  red  corpuscles  are  oval,  nucleated, 
and  usually  are  larger  than  those  of  mammals. 

What  are  microcytes? 

In  many  specimens  oi"  blood  are  observed  some  corpuscles  which 
are  smaller  than  the  rest :  they  are  called  microcytes,  and  are 
probably  immature  corpuscles.  One  form  is  of  especial  interest. 
They  are  of  about  one-third  the  size  of  ordinary  corpuscles,  not 
deeply  pigmented,  round  or  oval.  They  are  called  the  hlood-jilatoi 
of  Bizzozero,  and  have  been  affirmed  to  be  broken  up  to  form  the 
fibrin  ferment. 

What  is  the  origin  of  the  colored  corpuscles  ? 

This  is  somewhat  uncertain,  but  it  is  probable  that  red  corpuscles 
take  their  origin  from  colorless  nucleated  corpuscles  similar  to  if 
not  identical  with  white  corpuscles ;  possibly  also  from  the  nuclei 
of  white  globules,  from  the  tissue  of  the  spleen,  and  from  the 
marrow  of  the  bones. 

How  are  the  red  corpuscles  destroyed? 

Without  doubt,  the  red  corpuscles  have  a  definite  life,  and  when 
their  work  is  done  die  as  do  the  other  parts  of  the  body,  after  a 
tolerably  definite  existence.  Neither  the  length  of  their  life  nor 
the  manner  of  their  death  is  definitely  understood.  It  is  believed, 
and  partially  demonstrated,  that  they  undergo  disintegration  in  the 
spleen. 
What  is  the  number  of  the  red  blood-corpuscles  ? 

It  is  almost  beyond  estimate,  but  it  is  calculated  that  the  aver- 
age for  normal  human  blood  is  about  5,000,000  in  each  cubic 
millimetre.  In  practice  it  is  customary  to  estimate  the  number 
of  red  corpuscles  by  counting  the  corpuscles  in  a  minute  but 
measured  quantity  of  blood  spread  upon  a  ruled  microscope  slide. 
Such  an  instrument  is  known  as  a  hajmocytometer,  and  that  of 
Oowers  is  frecjuently  used. 

Describe  the  white  or  colorless  blood-corpuscles. 

They  are  spherical,  granular  masses  of  protoplasm,  possessing 
a  nucleus,  but  no  cell-wall.  They  are  about  YzaJi  "'•  ^"  diameter, 
though  some  appear  smaller,  and  are  probably  undeveloped  white 
corpuscles. 


26  THE    BLOOD. 

By  what  other  name  are  they  known  ? 

Leucocytes. 
What  is  their  proportion,  numerically,  to  the  red  corpuscles  ? 

The  proportion  is  1  to  500  or  600,  but  this  relation  is  varied  by 
conditions  of  health  and  disease,  by  age,  etc..  being  more  abun- 
dant in  youth,  in  anaemic  conditions,  in  pregnancy,  and  after  a  full 
meal. 

What  power  is  peculiar  to  white  corpuscles? 

The  power  of  amoeboid  movement,  by  which  they  are  able  to 
pass  through  the  walls  of  capillaries  into  the  surrounding  tissues. 
This  we  call  diapedesis.  The  physiological  value  of  this  is  not 
known. 

What  is  the  source  of  the  white  corpuscles  ? 

Leucocytes  come,  no  doubt,  from  the  lymph-glands,  in  which 
they  may  be  seen  in  large  numbers — "lymph-corpuscles" — and 
from  which  they  are  poured  into  the  blood.  They  also  originate 
by  fission.  Some  also,  probably,  are  derived  from  the  spleen  and 
from  the  thymus  gland,  perhaps  also  from  microcytes. 

What  is  the  ending  .of  the  leucocytes  ? 

Many,  probably,  are  decomposed  in  the  blood-vessels,  but  more 
end  as  colored  cells  ;  still  others  take  part  in  inflammatory  pro- 
cesses and  are  ended  in  this  way. 

What  are  the  uses  of  the  blood  ? 

(1)  To  receive  and  convey  food  and  oxygen  to  all  the  parts  of 
the  body. 

(2)  To  receive  from  the  organs  and  carry  away  the  refuse  mat- 
ters to  other  organs  whose  function  is  to  excrete  them. 

(3)  To  warm  and  moisten  all  parts  of  the  body. 

What  is  the  active  ingredient  of  the  blood  in  its  oxygen-carry- 
ing function? 

Haemoglobin.  In  the  lungs  the  haemoglobin  of  the  red  corpus- 
cles is  combined  in  loose  chemical  union  with  oxygen,  and  this 
union  is  broken  down  in  the  tissues  of  the  body. 

What  is  the  difference  between  arterial  and  venous  blood? 

(1)  Arterial  blood  is  bright  red  (scarlet)  from  the  combination 
of  haemoglobin  with  oxygen  (oxy-haemoglobin)  ;  and  venous  blood 
is  purplish  or  blue  from  deoxidation  of  the  oxy-haemoglobin. 

(2)  Arterial  blood  coagulates  somewhat  more  quickly. 


CIRCULATION   OF  THE    BLOOD.  27 

(3)  Arterial  blood  contains  more  oxygon  and  less  carbon  dioxide 
than  venous. 

What  is  the  chemical  basis  of  blood  ? 

Water  is  the  principal  constituent,  and  in  it  are  dissolved  salts 
and  proteid  matters,  and  suspended  in  it  are  the  corpuscles. 
Roughly,  the  composition  of  blood  may  be  tabulated  as  follows : 

Seruvi.  ,  Corpuscles. 

-  -      Water   .    .       .........  69 

Inorganic  salts  (chiefly  sodium 
chloride  and  potassium  phos- 
phate), 
Organic  matter, 

(Haemoglobin 27 

Proteids 2.7 

Fats 0.3) 


Water 90 

Proteids 8 

Salts 1 

Fats,  ] 

Glucose,         I  ■• 

Extractives,   f 

Pigment,        J  ^ 

100 


30 

100 


What  are  the  gases  of  the  blood  ? 

Carbonic  oxide,  oxygen,  and  nitrogen.  The  proportion  of  gases 
to  the  blood  is  about  one-half  the  volume.  Of  these,  carbonic  oxide 
is  greatly  in  excess  in  both  arterial  and  venous  blood.  The  propor- 
tion is  shown  in  the  tabular  form,  thus : 

Arterial  blood,  per  100  volumes,  CO^  39,  0^  20,  N  1  +  . 
Venous  blood,  per  100  volumes,  CO,  46,  0,  10,  N  1  +  . 

CIRCULATION  OF  THE  BLOOD. 

What  is  meant  by  the  circulation  of  the  blood? 

The  course  which  the  blood,  as  a  transporting  medium,  follows 
in  taking  food  and  air  to  the  tissues  and  bringing  away  the  used-up 
material  for  excretion,  returning  when  freshly  charged  with  oxygen 
and  food. 

Of  what  does  the  circulatory  apparatus  consist? 

(1)  The  heart,  which  propels  the  blood  ; 

(2)  The  arteries,  which  convey  it  from  the  heart  to  the  diiierent 
parts  of  the  body  ; 

(3)  The  capillaries,  a  network  of  inosculating  tubules  inter- 
woven with  the  substance  of  the  tissues  and  bringing  the  blood  into 
intimate  contact  with  it ; 

(4)  The  veins,  which  collect  the  blood  from  the  capillaries  and 
return  it  the  heart. 


28 


CIKCULATION   OF  THE   BLOOD. 


Fig.  1. 


Describe  the  course  of  the  blood  in 
circulation,  beginning  with  its 
entrance  into  the  left  auricle. 

Into  the  left  auricle  from  pul- 
monary veins,  thence  passing  the 
open  mitral  valve  into  the  left  ven- 
tricle (Fig.  1).  Upon  contraction 
of  the  ventricle  the  mitral  valve  is 
closed  and  the  aortic  valve  thrown 
open,  so  that  the  blood  is  thrown 
into  the  aorta,  and  thence  through 
the  systemic  arterial  circulation  into 
capillaries  and  on  into  veins,  the 
systemic  veins  finally  joining  to  fill 
the  venas  cavas,  and  from  them  the 
right  auricle.  From  the  right  auricle 
past  the  tricuspid  valve  into  the 
right  ventricle,  whence  it  is  thrown 
through  the  pulmonary  artery 
(guarded  by  the  pulmonary  semi- 
lunar valve)  into  the  pulmonary 
capillaries,  and  thence  into  the  pul- 
monary veins,  whence  it  started. 
Thus  we  have  in  reality  two  cir- 
culations, the  systemic  and  pul- 
monary. 

Describe  the  heart. 

The  heart  is  a  muscular  organ 
situated  in  the  thorax,  where  it  lies 
between  the  lungs  within  the  peri- 
cardial sac,  and  rests  upon  the  dia- 
phragm somewhat  to  the  left  of  the 
mid-line  of  the  body.  It  is  con- 
ical in  form,  and  is  so  suspended 
by  the  great  vessels  that  the  apex 
points  to  the  left  and  downward. 
Its  size  is  about  that  of  the  closed 
fist  (weight,  in  adults,  about  10 
ounces). 

Diagram  of  the  Circulation:  1,  heart;  2,  lungs;  3,  head 
and  upper  extremities;  4,  spleen;  5,  intestine;  6,  kid- 
ney ;  7,  lower  extremities ;  8,  liver. 


CIRCULATION   OF  THE   BLOOD. 


29 


What  are  its  cavities? 

It  is  divided  by  a  septum  into 
two  cavities,  not  connected,  the 
right  and  left  (Fig.  2).  Each 
of  tliese  in  turn  is  subdivided 
into  two  parts,  tlie  auricle  and 
the  ventricle.  The  auricU'S  arc 
thin-walled  cavities,  whose  func- 
tion is  to  receive  tiie  blood  from 
the  veins  and  pour  it  into  the 
ventricles.  The  ventricles  are 
the  most  powerful  portions  of 
the  heart-muscle,  the  left  being 
much  stronger  and  thicker  than 
the  riaht  ventricle. 


Fio.  2. 


Tran.svci'sc  SfLiion  ultlu'  lUillDck's  Heart  in 
the  State  of  Cadaverie  Kijiidity :  a,  cavity 
of  tlic  left  ventricle;  b,  cavity  of  the  riglit 
ventricle. 


What  is  the  capacity  of  these  cavities  ? 
Auricles,  about  4  oz. ;  ventricles,  about  6  oz. 

Fk;.  3. 


Course  of  lUooil  tlirouf,'li  the  Heart :  a,  it,  vena  cava,  superior  and  inferior ;  h,  right  ven- 
tricle ;  c,  luilnionary  artery  ;  </,  iniluionary  vein  ;  e,  left  ventricle  ;  /,  aorta. 

What  is  the  use  of  the  valves? 

To  allow  the  blood  to  pass  in   one  direction  only  through  the 
heart  (Fig.  4). 


30  CIRCULATIOK  OF  THE   BLOOD. 

Describe  the  structure  of  the  arteries. 

They  are  surrounded  by  a  dense  fibrous  coat  externally,  and 
lined  internally  by  a  smooth  serous  (endothelial)  lining }  between 

Fig.  4. 


Valves  of  the  Heart. 

these  is  an  elastic  layer  of  fibrous  tissue,  which  has  interlaced  in 
its  structure  muscle-cells.  Each  artery  has  its  own  vasa  vasorum, 
or  nutrient  vessels,  and  is  usually  enmeshed  in  a  plexus  of  sympa- 
thetic nerves,  "  vaso-motor  nerves." 

Describe  the  capillaries. 

The  capillary  blood-vessels  are  channels  of  very  small  but 
variable  size,  but  usually  of  about  sufficient  calibre  to  just  permit 
the  passage  of  the  red  and  white  corpuscles.  They  are  usually 
composed  of  a  single  layer  of  endothelial  cells  joined  at  the  edges, 
though  near  the  arteries  and  veins  there  is  sometimes  an  elastic 
fibrous  coat.  A  sympathetic  nerve-plexus  surrounds  these  vessels. 
The  capillaries  form  a  complicated  network  in  the  tissues,  and  the 
mesh  of  the  net  varies  in  shape  and  size  greatly  with  the  vascu- 
larity and  function  of  the  tissue. 

Describe  the  characteristics  of  the  veins. 

In  structure  the  veins  are  similar  to  the  arteries,  but  much  less 


CIRCULATION   OF   TlIK   BLOOD. 
Fw.  5. 


31 


Capillary  Plexus  in  a  Portion  of  the  Web  of  a  Frog's  Foot  (magnified  110  diameters) :  1, 
trunk  of  vein  ;  2,  2,  2,  its  branches;  3,  3,  pigmeut-cells. 

firm  and  elastic ;  veins  collapse,  while  arteries  remain  open  when 
not  distended  by  blood.  Valves  occur  in  most  of  the  veins  ;  these 
are  so  placed  as  to  prevent  the  blood  from  tending  to  flow  back- 
ward. The  valves  are  so  placed  as  to  aid  the  onward  progress  of 
the  blood  in  the  veins,  the  pressure  of  neighboring  muscles  forcing 
forward  the  blood,  which  cannot  regurgitate  past  the  valves. 

What  is  the  relative  area  of  arteries,  capillaries,  and  veins  ? 

With  the  divisiuii  of  the  arteries  into  branches  the  sectional 
area  of  the  branches  is  greater  than  of  the  stem.  Of  the  veins 
the  same  is  true,  while  the  total  sectional  area  of  the  capillary 
system  is  much  greater  than  of  either.  For  purpo.ses  of  simile  the 
comparison  may  be  made  of  two  funnels  placed  base  to  base.  In 
numbers  one  may  consider  the  sectional  area  of  aorta  as  1  ;  of 
venae  cavae,  2  or  3 ;  of  capillaries,  (about)  800. 


32  CIUCULATION  OF  THE  BLOOD. 

Describe  the  action  of  the  auricles. 

During  the  period  of  rest  of  the  heart  blood  flows  freely  from 
the  veins  into  the  ventricles,  the  auriculo-ventricular  valves  offer- 
ing no  resistance  ;  but  the  influx  is  so  strong  that  by  the  time  the 
heart  begins  to  contract  the  auricle  is  quite  filled  and  the  ventricle 
partially.  The  contraction  of  the  auricle  is  sudden  and  very  quick, 
comrriencing  at  the  great  veins  and  extending  toward  the  ventricu- 
lar opening.     Both  auricles  contract  simultaneously. 

Why  does  not  the  auricle  throw  the  blood  back  into  veins  ? 

(1)  The  power  of  the  auricular  contraction  is  not  sufficient  to 
cause  a  reflux. 

(2)  The  muscular  coat  of  the  great  veins  near  the  heart  con- 
tracts, and  helps  to  prevent  this  regurgitation. 

(3)  The  weight  of  the  incoming  blood  opposes. 

(4)  Valves  in  the  veins  oppose,  and  the  Eustachian  valve  guards 
the  inferior  vena  cava. 

Describe  the  action  of  the  ventricles. 

The  ventricle  is  distended  during  its  period  of  rest  by  the  flow 
of  the  blood  from  the  veins  and  by  the  auricular  contraction  ;  and 
its  contraction  seems  continuous  with  that  of  the  auricle,  so  imme- 
diately does  it  succeed.  The  ventricular  contraction  is  slower,  and 
probably  completely  empties  the  cavity.  The  ventricles  contract 
simultaneously.  The  shape  of  the  ventricles  is  changed :  as  the 
heart-muscle  becomes  hard  and  rigid  in  contraction,  the  section  of 
its  base  becomes  circular  instead  of  elliptical,  as  it  is  during  re- 
pose ;  the  ventricles  shorten  and  twist  to  the  right,  and  the  form  is 
conical.  As  the  organ  relaxes,  it  turns  back  to  its  former  position 
and  shape,  that  of  a  cone  with  elliptical  base.  This  shortening  of 
the  ventricles  in  contraction  is  compensated  by  the  lengthening  of 
the  great  vessels  at  the  base  as  they  become  distended  by  the  load 
of  blood.* 

What  are  the  functions  of  the  valves  of  the  heart  ? 

In  considering  the  functions  of  the  valves  of  the  heart  one 
must  bear  in  mind  constantly  that  the  organ  is  a  pump  whose 
office  is  to  force  the  blood  in  one  direction.  There  are  four 
principal  valves — two  auriculo-ventricular.  and  two  in  the  great 
arteries,  the  aorta  and  the  pulmonary  artery.  (1)  As  the  ventricle 
fills,  the  auriculo-ventricular  valves  are  floated  up  from  the  sides  of 

*  Some  physiologists  deny  the  shortening  of  the  ventricles  in  systole. 


CIRCULATION  OF  THE   BLOOD.  33 

tlie  ventricle  in  sucli  manner  that  tlieir  edges  are  in  contact,  cusp 
to  cusp.  As  the  ventricle  contracts  more  violently,  pressure  is 
hrouglit  to  bear  upon  the  valve,  so  that  not  only  is  the  edge  in 
contact,  but  also  portions  of  the  surfaces  of  the  cusps.  These 
valves  are  of  considerable  area,  and  are  guyed  in  position  by  the 
chnrdse  tetullnex,  which  spring  from  the  papillary  muscles,  so  that 
evcrsion  of  the  valve  into  the  auricle  is  impossible.  (2)  The 
semilunar  ralrcs  form  a  guard  against  the  return  of  blood  to  the 
ventricle  at  the  pulmonary  and  aortic  openings  of  the  ventricles. 
These  valves  are  forced  open  by  the  ventricular  contraction,  and 
through  them  the  blood  rushes  to  distend  the  elastic  walls  of  the 
large  arteries.  The  pressure  of  the  blood  under  this  elastic  grasp 
is  sufficient  to  throw  the  cusps  of  the  valves  into  action.  The 
corpora  Arantii  are  useful  in  making  a  perfect  closure  of  the  valve, 
though  not  absolutely  essential.  A  part  of  the  weight  of  this 
pressure  is  borne  by  the  thick  ventricular  wall,  from  the  outer 
edge  of  which  the  artery  springs,  while  the  valves  are  attached  to 
the  inner  edge. 

What  is  meant  by  the  safety-valve  action  of  the  tricuspid  valve  ? 

Under  some  circumstances  the  tricuspid  valve  does  not  entirely 
close,  but  allows  a  certain  amount  of  regurgitation  of  blood.  This 
is  in  conditions  of  disease  or  of  violent  exertion,  in  which  the  lung 
capillaries  are  overcharged  with  blood.  This  leakage  of  the  valve 
is  conservative,  by  relieving  the  pressure  upon  the  delicate  capilla- 
ries of  the  alveolae.  Pulsation  in  the  jugular  veins  indicates  this 
regurgitation.  The  condition  is  not  pathological,  and  with  altered 
conditions  disappears. 

What  terms  are  used  to  describe  the  alternate  contraction  and 
relaxation  of  the  heart  ? 

Systole,  a  contraction  ;  diastole,  a  relaxation 

What  is  meant  by  the  period  of  repose  ? 

Between  the  contractions  of  the  heart-muscle  there  is  a  percep- 
tible pause,  which  has  been  called  the  period  of  repose.  If  the 
time  of  a  cycle  be  divided  into  five  parts,  the  systole  of  auricles 
will  employ  1  part ;  systole  of  ventricles,  2  parts  ;  period  of  repose, 
2  parts.  The  accuracy  of  this  division  is  not  absolute,  for,  whatever 
the  pulse-rate,  the  ventricular  systole  consumes  nearly  four-tenths 
of  a  second. 

3— Phy. 


34  CIRCULATION   OF  THE   BLOOD. 

Describe  the  heart-sounds. 

The  first  sound  is  heard  best  over  the  apex  of  the  heart.  It  is 
of  a  dull,  prolonged,  booming  character.  The  second  sound  is  heard 
immediately  after  the  first,  and  is  a  sharp,  quick,  almost  clicking 
sound  ;  it  is  heard  most  clearly  over  the  base.  The  sounds  are  said 
to  somewhat  resemble  that  expressed  by  luhh-dup. 

What  is  the  cause  of  the  heart-sounds  ? 

The  origin  of  the  first  sound  of  the  heart  is  not  fully  explained ; 
but  as  it  is  synchronous  with  the  ventricular  systole  and  with  the 
closure  of  the  auriculo-ventricular  valves,  it  is  supposed  to  be  due 
to  muscular  action  and  vibration  of  auriculo-ventricular  valves  and 
chordae  tendineae.  The  second  sound  is  synchronous  with  the 
closure  of  the  semilunar  valves,  and  is  caused  by  this  action. 

What  is  the  normal  frequency  of  the  heart's  action  ? 

At  birth,  about  130  per  minute. 

At  three  years,    "      100    "        " 

In  adult  life,        "        75    "        " 

In  old  age,  "        65    "        " 

This  rate  is  varied  from  time  to  time  by  conditions  of  bodily 
health  and  by  environment.  The  heart  in  women  is  somewhat 
more  rapid  than  in  men.  After  eating,  during  exercise,  in  a  hot  or 
rarefied  atmosphere  the  heart  is  more  rapid.  The  relative  frequency 
of  heart  and  respiratory  action  is  about  three  or  four  heart-beats 
to  one  respiratory  act. 

What  force  does  the  heart  exert  in  systole? 

The  left  ventricle  exerts  more  than  twice  as  much  power  as  the 
right.  The  exact  intraventricular  pressure  in  man  has  not  been  as- 
certained. The  expansion  of  the  heart  exerts  a  negative  (or  suc- 
tion) pressure,  which  aids  the  onfiow  of  the  blood,  especially  from 
the  lungs  to  the  left  ventricle.  The  intra-auricular  pressure  is  very 
much  less  than  the  intraventricular,  and  there  is  a  negative  pres- 
sure during  diastole  in  the  auricles. 

What  is  the  estimated  work  of  the  heart  in  systole  ? 

Estimated'  in  foot-pounds,  each  ventricular  contraction  repre- 
sents 3^  to  4j  foot-pounds.  In  twenty-four  hours  this  is  estimated 
to  equal  more  than  120  foot-tons.  In  another  light,  if  the  blood  is 
one-twelfth  of  the  body-weight,  and  if  the  amount  of  blood  pumped 
with  each  ventricular  contraction  is  6  oz.,  in  an  ordinary  man  an 


CIRCULATION  OF  THE   BLOOD.  35 

amount  of  blood  equal  to  the  total  blood  of  the  body  will  pass 
tliroutrli  the  heart  in  about  half  a  luiuuto. 

What   are  influences  of  the  nervous    system   upon  the  heart's 
action  ? 

This  matter  is  somewhat  undecided  at  tlie  i)resent,  fur  the  reason 
that  many  of  the  results  must  be  obtained  from  experiments  upon 
the  hearts  of  cold-blooded  animals.  We  do  know  that  the  mechan- 
ism of  rhythmical  contraction  is  contained  within  the  heart  itself. 
Nerve-ganglia  are  demonstrated  in  the  frog's  heart  which  are  essen- 
tial to  its  action  ;  presumably  similar  ganglia  exist  in  the  human 
heart.  These  ganglia  are  connected  with  fibres  from  the  pneumo- 
gastric  (or  vagus)  nerve  and  with  the  sympathetic  system. 

What  is  the  effect  of  the  pneumogastric  nerve  upon  the  heart? 

It  has  an  inhibitoiy  or  slowing  effect  upon  the  heart ;  for  if  we 
cut  the  nerve  the  heart  becomes  more  rapid,  and  if  we  stimulate 
the  peripheral  end  of  the  nerve  we  slow  the  heart  again.  This 
action  may  be  traced  to  the  medulla  oblongata,  where  a  cardio-inhib- 
itory  centre  is  located. 

What  is  the  relation  of  the  heart  to  the  sympathetic  nervous 

system  ? 
Certain  fibres  of  the  sympathetic  from  the  cervical  and  upper 
dorsal  spinal  cord  pass  to  the  heart.  If  these  fibres  are  left  after 
all  other  nerve-connections  of  the  heart  are  cut  away,  stimulation 
of  the  spinal  cord  will  cause  the  heart  to  become  rapid.  These  are 
known  as  accelerator  nerves. 

What  is  meant  by  the  pulse? 

The  wave  which  is  felt  in  an  artery  after  the  systole  of  the 
ventricle. 

What  is  a  sphygmograph  ? 

An  instrument  used  to  trace  mechanically  a  diagram  of  the 

pulse-wave. 

How  is  the  heart  nourished? 

Hy  the  coronary  arteries,  which  arise  in  the  sinuses  of  Valsalva 
behind  the  leaves  of  the  semilunar  valve.  They  do  not  receive  blood 
during  systole,  but  during  diastole  from  the  pressure  of  blood  in  the 
elastic  arteries.  The  blood  is  returned  to  the  right  auricle  through 
the  coronary  vein. 


36  EESPIRATIOlSr. 

What  causes  unite  to  compel  the  return  of  the  blood  through 
the  veins? 

(1)  Vis  a  tergo,  or  the  pressure  remaining  from  the  force  of  the 
left  ventricular  systole  and  arterial  elasticity. 

(2)  Muscular  action  in  pressing  upon  the  veins  which  have  valves. 

(3)  Suction  Poioer  of  the  Heart. — During  diastole  the  opening  of 
the  heart-cavity  is  sufficiently  strong  to  exert  a  rather  strong  "  neg- 
ative pressure  "  or  suction  power. 

(4)  Aspiration  (or  suction)  power  of  the  chest  in  respiration. 

(5)  The  slight  rhythmical  contractions  of  the  veins. 

What  is  meant  by  vital  capillary  force  ? 

The  capillaries  are  not  unchanging  blood-channels,  but  may  be 
seen  to  dilate  and  contract  under  the  influence  of  stimuli.  We 
have  seen  that  each  capillary  has  its  accompanying  vaso-motor 
sympathetic  plexus ;  and  this  it  is  which  controls  this  force,  seen 
in  blushing,  pallor,  etc. 

What  is  arterial  tension? 

The  walls  of  the  arteries  being  very  elastic,  and  the  blood  being 
forced  into  them  at  considerable  pressure,  permits  them  to  keep  the 
blood  under  elastic  compression  within  the  arteries,  so  that  when 
an  artery  is  cut  the  blood  spurts  from  it  in  a  jet.  The  capillaries, 
though  collectively  of  much  greater  area  than  the  arteries,  by  rea- 
son of  the  friction  they  offer  to  the  blood-stream  maintain  a  less 
degree  of  tension. 

What  causes  modify  the  arterial  tension  ? 

(1)  The  rate  of  the  heart-beats,  by  keeping  the  arteries  fuller  or 
less  full,  will  modify  the  blood-pressure  in  the  arteries. 

(2)  Vaso-motor  changes,  by  increasing  or  decreasing  the  friction 
offered  the  arterial  blood,  vary  the  tension  in  the  arteries. 

(3)  The  amount  of  blood  in  the  system  must  to  a  great  extent 
determine  the  limits  of  arterial  pressure.  In  great  exsanguination 
the  arterial  pressure  is  quite  low. 

(4)  Motion  of  the  thoracic  walls  in  breathing  necessarily  changes 
the  arterial  tension  by  the  pumping  force  exerted  by  this  motion. 

RESPIRATION. 
What  constitutes  respiration? 

By  respiration  we  mean  the  process  by  which  oxygen  is  intro- 
duced to  the  system  and  by  which  carbonic  oxide  is  excreted. 


RESPIRATION.  37 

This   function    is   performed    in    the   lungs,    and    the    transfer   is 
effected  by  the  agency  of  the  blood. 

Describe  the  course  of  the  air  in  entering  the  lungs. 

Air  is  taken  through  the  nose  (ir  mouth,  and  passes  through  the 
l)liarynx  to  the  larynx  ;  entering  the  rinia  glottidis,  it  passes  through 
the  larynx  to  the  trachea  and  bronchi.  The  air  is  somewhat  warmed 
and  moistened  in  its  passage.  The  trachea  and  bronchi  are  lined 
with  ciliated  epithelium,  which  serves  to  sweep  particles  of  dust 
and  the  like  out  of  the  air-passages. 

Describe  roughly  the  minute  anatomy  of  the  lung. 

Each  lobe  of  the  lung  is  composed  of  numerous  lobules,  to  each 
of  which  a  small  bronchiole  enters,  and  the  minute  terminal  branches 
of  these  bronchioles  (^infundlhuhi)  widen  into  a  sort  of  ii'regular 
funnel  having  pouched  or  saccuhited  dilatations  known  as  air- 
cells.  These  air-cells  are  supported  by  numerous  elastic  fibres,  and 
are  lined  with  a  very  thin  layer  of  flat  (not  ciliated)  epithelium. 
Outside  the  epithelial  lining  is  a  very  clo.se  mesh  of  capillaries, 
which  are  often  exposed  to  air  on  both  sides  by  lying  in  a  partition 
between  two  of  the  air-cells.  The  air-cells  or  vesicles  are  about  gig- 
in.  in  diameter,  and  the  space  between  the  capillaries  is  often  less 
than  the  diameter  of  a  capillary. 

What  is  the  blood-supply  of  the  lungs  ? 

There  are  two  sources  :  (1)  from  the  bronchial  arteries  (systemic) 
for  nutrition  ;  (2)  from  pulmonary  artery  for  oxidation. 

How  is  air  introduced  to  the  lungs? 

The  thoracic  cavity  in  which  the  lungs  lie  being  a  closed  cavity, 
the  expansions  of  its  walls  will  tend  to  create  a  partial  vacuum 
in  its  interior.  It  is  by  this  means  that  air  is  introduced.  This 
expansion  of  the  chest-wall  (and  with  it  the  lung)  we  call  inspira- 
tion. Contraction  of  the  cavity  of  the  thorax  tends  to  cause  com- 
pression of  its  contents,  and  thus  to  expel  the  contained  air:  this 
we  call  expirdtion.     The  complete  act  is  called  i-esjxirafioji. 

Describe  briefly  the  mechanism  of  respiration. 

A.  Jiispinitioii. — 'J'hc  diameters  of  the  thoracic  cavity  are  all  in- 
creased— (1)  the  vertical  by  the  action  of  the  diaphragm  ;  (2)  the 
lateral  and  antero-posterior  diameters  by  the  elevation  of  the  ribs. 
Thus  we  may  have  a  diaphragmatic  or  abdominal  type  of  breath- 


38  RESPIRATION. 

ing  and  a  costal  or  ctest  type  ;  the  former  is  characteristic  of  men, 
the  latter  of  women. 

B.  In  expiration  the  natural  elasticity  of  the  lungs  and  the  chest- 
wall  causes  very  little  muscular  action  to  be  needed  in  natural 
expiration.  In  forced  expiratory  efforts  all  muscles  which  depress 
the  ribs  may  be  called  into  action  here. 

What  is  the  force  of  the  respiratory  effort  ? 

The  average  man  is  able  to  elevate  a  column  of  mercury  in  a 
manometer  tube  2\  to  3  inches  by  an  effort  at  inspiration.  In 
expiration,  when  forced,  the  mercury  will  range  about  an  inch 
higher,  but  it  should  be  remembered  that  many  muscles  which  are 
ordinarily  used  for  other  purposes  may  be  called  into  play  in  this 
effort. 

What  is  meant  by  the  term  "  vesicular  murmur  "  ? 

It  is  the  sound  heard  in  listening  over  a  normal  lung  during 
respiration,  and  is  described  as  a  soft  sighing  sound  heard  at  the 
instant  air  enters  the  alveoli.  Its  cause  is  not  fully  understood, 
but  it  is  supposed  to  be  due  to  the  friction  of  the  air  against  the 
walls  of  the  vesicles. 

What  is  tidal  air  ? 

The  amount  of  air  which  is  habitually  changed  in  an  ordinary 
act  of  breathing.  In  forced  inspiration  the  excess  of  air  is  known 
as  compleniental  air. 

What  is  reserve  air? 

The  air  left  in  the  lung  after  ordinary  expiration.  After  forced 
expiration  there  always  remains  a  certain  amount  of  air,  known  as 
residual  air. 

What  is  the  respiratory  capacity? 

The  greatest  quantity  of  air  which  one  can  drive  from  the  lungs 
after  forced  inspiration :  this  is  about  225  cubic  in.  in  an  average 
adult  man.  The  tidal  air  for  the  same  man  will  be  about  30  cubic 
in.  These  figures  are  not  constant,  and  vary  with  conditions  of 
health,  figure,  age,  sex,  and  atmospheric  conditions. 

What  is  the  normal  rapidity  of  the  respiration  ? 

In  a  healthy  adult  14  to  18  per  minute.  In  infants  and  invalids 
the  rate  is  often  much  more  rapid.  The  ratio  to  the  pulse-rate  is 
about  1  to  5  in  the  healthy  individual. 


RESPIRATION.  39 

Describe  the  rhythm  of  respiration. 

The  respirator}'  aet  is  rliytliiiiical,  inspiration  bcin,2j  Rlifrbtly  more 
ra])i(l  tliaii  expiration,  a  slight  pause  occurring  after  expiration 
het'orc  a  fresh  breath  is  drawn. 

Describe  the  movements  of  the  nostrils  and  larynx  in  respira- 
tion. 

With  every  inspiration  (especially  if  rapid)  there  is  dilatation  of 
the  nostrils  and  a  partial  closure  during  expiration.  The  rima  glot- 
tidis  is  in  the  same  way  opened  for  the  ingress  of  air.  This  is  like 
the  respiratory  act,  in  that  the  opening  is  a  muscular  act  during 
inspiration,  and  the  recoil  elastic  in  ordinary  breathing. 

What  is  the  composition  of  the  atmosphere  ? 

It  has  a  nearly  unil'urm  composition. 

By  Volume.  By  Weight. 

Oxygen,    79  parts.  75  parts. 

Nitrogen,  21     "  25     " 

Carbonic  acid,  .04. 
Ammonia  and  impurities,  trace. 

What  is  the  temperature  of  expired  air? 

The  expired  air  is  at  about  the  temperatui'c  of  the  body,  what- 
ever its  temperature  when  inspired. 

How  much  carbonic  acid  does  exhaled  air  contain? 

While  ordinary  air  contains  only  about  •]  a  part  of  carbonic  acid 
])er  1000,  expired  air  is  found  to  contain  about  43  parts  per  1000 
of  COa-  This  is  varied  by  conditions  of  health  and  disease,  age, 
atmospheric  conditions,  and  a  number  of  other  causes. 

How  much  oxygen  is  taken  from  the  air  in  respiration? 

The  oxygen  of  the  exhaled  air  is  decreased  in  about  the  same 
ratio  that  its  carbonic  acid  is  increased  (roughly  5  per  cent.).  This 
proportion  is  not  exact,  as  there  is  some  excess  of  oxygen  which  is 
absorbed  in  the  system  and  does  not  reappear  as  00.^. 

How  much  water  appears  in  expired  air? 

The  amount  varies  with  the  atmospheric  conditions  as  well  as 
bodily  changes,  but  ordinarily  in  a  day  about  10  ounces  of  water  in 
the  form  of  vapor  are  found  in  expired  air  in  excess  of  that  normally 
present.  This  may  amount  to  30  ounces,  or  fall  as  low  as  G 
ounces. 


40  RESPIRATION. 

Mention  some  other  changes  in  the  respired  air. 

Small  quantities  of  organic  matter  and  of  ammonia  are  found. 

Has  the  nitrogen  of  the  air  a  physiological  bearing? 

A  small  amount  of  this  gas  is  found  in  the  blood,  but  it  is 
mostly  in  simple  solution,  and  is  not  supposed  to  be  of  physio- 
logical value.  In  respired  air  it  is  of  use  as  a  diluent  of  the 
oxygen. 

Describe  the  respiratory  changes  of  the  air  in  the  lungs. 

In  the  blood  oxygen  is  in  loose  chemical  combination  with  the 
haemoglobin  (oxy-haemoglobin).  The  amount  of  the  oxygen  in  the' 
residual  air  of  the  pulmonary  alveoli  is  estimated  at  about  10  per 
cent.,  that  of  expired  air  being  16  per  cent.  It  is  found  that  unless 
there  is  present  about  4  per  cent,  of  oxygen  there  is  no  tendency  for 
the  blood  of  the  pulmonary  arteries  (venous)  to  take  up  fresh  oxygen, 
or  the  tension  of  the  oxygen  in  the  reduced  hasmoglobin  of  venous 
blood  is  about  4  per  cent.,  and  unless  the  oxygen  tension  in  the 
lungs  is  greater,  there  is  no  absorption  of  oxygen.  But,  as  we 
have  seen,  the  amount  of  oxygen  amounts  to  at  least  10  per  cent., 
and  therefore  the  excess  is  sufficient  to  exceed  the  demands,  and 
the  exchange  is  readily  made  by  diffusion  through  the  thin  capil- 
lary walls  in  the  alveoli. 

On  the  other  hand,  the  tension  of  the  carbonic  acid  in  the 
pulmonary  arteries  is  much  higher  than  in  the  alveoli,  and  hence 
the  extrusion  of  this  gas  by  diffusion  is  accomplished. 

How  is  the  blood  changed  by  respiration  ? 

(1)  Color,  deep  purple  to  bright  scarlet  by  oxidation  of  the 
reduced  haemoglobin — i.  e.  from  venous  becomes  arterial  blood ; 
(2)  gains  oxygen  ;  (3)  loses  carbonic  acid ;  (4)  becomes  cooler ; 
(5)  coagulates  more  readily. 

Name  some  of  the  special  actions  of  modified  respiration. 

There  are  a  number  of  involuntary  and  voluntary  special  respi- 
ratory acts,  largely  reflex,  which  are  dependent  upon  modifications 
of  inspiration  and  expiration — e.  g.  sighing,  hiccough,  cough,  sneez- 
ing, speaking,  singing,  sniffing,  sobbing,  laughing,  yawning. 

What  is  the  nervous  mechanism  of  respiration  ? 

i        In  the  medulla  oblongata  are  centres  for  each  half  of  the  body, 

)(    from  which  arise  automatically  the  rhythmical  impulses  for  the 

respiratory  acts.     While  these  are  automatic,  they  may  be  stimu- 


RESPIRATION.  41 

lated  by  reflex  influence.  The  nerves  which  convey  to  the  muscles 
of  inspiration  their  impulse  are  tlie  plirenics  (to  the  diaphragm) 
and  tlie  intercostals  (to  the  intercostal  muscles).  The  reflex  stimuli 
are  conveyed  l)y  the  pncuniogastric  nerve,  and  are  twofold  :  by  the 
main  trunk  of  the  nerve  the  inspiratory  efforts  are  excited,  and  by 
the  superior  laryngeal  l)ranch  expiratory  reflexes  are  obtained. 
Thus  stimulation  of  the  superior  laryngeal  nerve  may  be  said  to 
inhibit  the  inspiratory  centre  and  to  excite  the  expiratory  centre, 
while  the  contrary  may  be  said  of  the  main  trunk  of  the  nerve. 

How  is  the  vagus  excited  to  this  reflex  activity? 

While  the  respiratory  centres  seem  to  act  automatically,  yet  in 
certain  conditions,  in  which  oxygen  is  wanting  in  the  blood,  the 
absence  of  oxygen  (not  the  presence  of  carbonic  acid)  stimulates 
the  respiratory  centres,  through  the  pneumogastric  filaments  in  the 
lungs,  to  increased  activity.  This  reflex  activity  results  in  forcible 
respirator}^  efforts  which  we  call  dijs^pnaa.  It  is  not  known  whether 
this  reflex  arises  from  the  absence  of  oxygen  from  the  air  of  the 
alveoli  or  from  the  blood  of  the  pulmonary  capillaries. 

What  are  the  symptoms  of  lack  of  oxygen  in  the  blood  ? 

If  the  need  be  only  moderate,  there  will  be  increased  effort  of 
both  expiration  and  inspiration,  and  the  respirations  will  be  rapid — 
a  condition  known  as  hyprrpnoea.  As  the  oxygen  becomes  less  and 
less  abundant  the  symptoms  become  moi'e  severe,  and  the  condition 
is  known  as  di/sjmo'a.  The  dyspnoea  increasing,  the  respiratory 
eff"orts  become  very  violent,  and  the  condition  of  nxpltijxia  is  seen. 
In  this  the  face  is  blue,  eyes  starting,  face  anxious,  and  respirations 
very  rapid  and  strident.  Then  follows  a  convulsive  condition  which 
is  brief,  the  convulsions  being  very  violent  and  involving  the  entire 
body.  After  this  the  patient  lapses  into  a  state  of  exhaustion,  in 
which  the  respirations  are  slow,  very  feeble,  and  the  general  con- 
dition is  one  of  collapse.     Death  ensues  very  soon. 

How  is  air  vitiated  by  lack  of  ventilation  ? 

In  ill-ventilated  rooms  the  air  of  the  room  is  used  repeatedly, 
and,  besides  becoming  partially  deprived  of  its  oxygen,  is  charged 
with  carbonic  acid  and  with  putrescible  nitrogenous  organic  mat- 
ters. This  causes  an  atmosphere  which  is  intolerable  to  one  who 
enters  from  fresh  air.  That  such  a  condition  is  unsanitary  needs 
no  argument. 


42  DIGESTION. 

What  are  the  requirements  for  good  ventilation? 

It  is  generally  accepted  as  a  fact  that  about  1000  cubic  feet  of 
air-space  per  head  must  be  allowed  in  sleeping  quarters,  and  suffi- 
cient facilities  for  exchange  of  air  to  allow  complete  change  in  each 
hour.  This  ventilation  must  be  accomplished  without  exposure  to 
draughts. 

What  effect  has  respiration  upon  the  circulation  ? 

Each  inspiration  causes  a  partial  vacuum  in  the  thoracic  cavity, 
and  hence  it,  so  to  speak,  sucks  the  blood  to  the  heart  from  the 
great  veins.  Each  expiration  does  not,  however,  check  the  flow 
of  blood,  for  the  expiration  does  not  increase  the  air-pressure,  but 
simply  returns  to  the  normal.  The  inspiration,  then,  increases 
arterial  tension  by  facilitating  the  venous  return. 

DIGESTION. 
What  is  digestion? 

By  this  term  we  indicate  the  process  by  which  food  is  introduced 
to  the  body  and  prepared  in  such  way  that  it  becomes  suitable  for 
absorption  and  tissue-nutrition.  The  process  may  be  divided  logi- 
cally and  conveniently  into  mastication,  insalivation,  deglutition, 
stomach  digestion,  intestinal  digestion,  and  defecation. 

Describe  mastication. 

When  a  mass  of  food  enters  the  mouth  it  is  caught  by  the  tongue 
and  moved  to  a  position  such  that  it  may  be  crushed  and  ground 
between  the  upper  and  lower  teeth.  This  process  is  favored  by 
the  action  of  the  tongue  and  of  the  cheeks,  which  not  only  crush 
the  softer  food-masses,  but  bring  the  less  tractable  portions  re- 
peatedly under  the  action  of  the  teeth. 

Describe  the  teeth. 

There  are  during  life  two  sets  of  teeth,  temporary  and  permanent. 
In  the  first  set  are  20  teeth,  and  in  the  second  32.  The  perma- 
nent set  are  arranged  as  follows  : 

Molar.        Bicuspid.        Canine.        Incisor.        Canine.       Bicuspid.        Molar. 

Upper. 3 2 1 4 1 2  3 

Lower.  3  2  14  1  2  3     " 

The  tooth-structure  resembles  bone  in  anatomical  as  well  as  chemi- 
cal view.  The  central  portion,  or  cement^  is  true  bone,  and  about 
it  is  a  somewhat  harder  layer  called  dentine.  Outside  of  all  is  a 
very  dense  layer  of  enamel. 


DIGESTION.  43 

What  muscles  are  involved  in  the  act  of  eating  ? 

Biting  nioveuioiits  arc  prodiu'cd  by  action  of  the  temporal,  nias- 
sotcr,  and  internal  pterygoid  muscles,  opposing  the  depressors  of 
the  jaw  ;  grinding  movements  are  produced  by  the  alternate  action 
of  the  external  pterygoids.  The  action  is  to  some  extent  reflex, 
though  largely  voluntary,  and  is  controlled  in  the  medulla  through 
branches  of  the  cranial  nerves,  motor  impulses  coming  through 
branches  of  the  trigeminus  and  (to  the  tongue)  hypoglossal  nerves. 

What  do  we  mean  by  the  term  "  insalivation  "  ? 

The  mixing  and  thorough  moistening  of  the  food-mass  with  the 
saliva  and  mucus  in  the  mouth  d.uring  the  act  of  chewing  is  called 
insalivation. 

What  is  the  saliva? 

The  saliva  is  derived  almost  entirely  from  the  parotid,  submax- 
illary, and  sublingual  glands,  and  is  secreted  most  abundantly 
during  mastication  of  food.  It  is  a  transparent  watery  fluid,  and 
is  somewhat  viscid  from  the  mixture  of  mucus.  This  viscidity 
allows  it  to  retain  air-bubbles  when  churned  by  the  action  of  the 
tongue  and  cheeks.  It  has  a  sp.  gr.  of  about  1006  and  an  alkaline 
reaction.  Chemically,  it  is  mostly  (99 2  per  cent.)  water,  holding 
in  solution  very  small  amounts  of  salts  and  proteids,  with  the  addi- 
tion of  a  ferment  called  ptyalin.  The  amount  secreted  in  twenty- 
four  hours  is  estimated  to  be  1  to  2  quarts,  most  abundant  secretion 
occurring  during  mastication. 

What  is  the  use  of  saliva  ? 

It  keeps  the  mouth  in  a  moist  condition,  and  so  lubricates  the 
tongue  in  speaking  and  in  chewing ;  dissolves  the  soluble  portions 
of  the  food,  and  in  this  way  brings  them  in  contact  with  the  organs 
of  taste  ;  mixes  with  the  food,  and  forms  a  soft  and  slippery  bolus 
suitable  for  swallowing.  Saliva  from  the  front  of  the  mouth,  con- 
taining more  water,  softens  the  bolus,  while  the  tonsillar  and 
pharyngeal  secretions,  being  mucous,  coat  it  with  a  slippery  sur- 
face ;  and  the  saliva  has  a  special  digestive  function  by  the  action 
of  its  ferment,  ptyalin. 

What  is  the  action  of  ptyalin  ? 

Ptyalin  is  a  ferment  (a  non-nitrogenous  body  having  an  uncer- 
tain chemical  composition),  with  the  s]»ecial  property  of  converting 
cooked  starch  into  grape-sugar,     ^\'hil('  the  ferment  it.self  cannot 


44  DIGESTION. 

be  isolated  and  analyzed,  a  glycerin  solution  may  be  obtained  from 
salivary  glands  which  have  been  dehydrated  by  alcohol.  This 
ferment  does  not  act  upon  any  other  body  than  starch.  The  action 
of  the  ferment  in  changing  starch  to  sugar  is  known  as  an  amylo- 
lytic  action,  and  such  a  ferment  is  called  an  amylolytic  ferment. 
The  kind  of  sugar  resulting  from  the  action  of  ptyalin  is  grape- 
sugar  or  glucose,  maltose  being  found  as  an  intermediate  step  in 
the  ferment's  action. 

At  what  age  do  the  salivary  glands  become  active  ? 

At  four  to  six  months ;  hence  the  reason  for  avoiding  starchy 
food  for  young  infants. 

What  tests  are  used  to  determine  the  presence  of  sugar  and  of 
starch  ? 

For  starch  an  entirely  reliable  and  simple  test  is  that  by  iodine : 
a  blue  color  follows  the  reaction  ;  it  is  a  very  delicate  test.  For 
sugar  Moore's  and  Fehling's  tests  depend  upon  the  reduction  of  a 
copper  solution,  and  are  quite  delicate.  The  fermentation  test  is  of 
value  in  accurate  quantitative  determination  of  sugar. 

What  is  the  action  of  the  nervous  system  upon  the  salivary 
glands  ? 

Saliva  is  secreted  more  abundantly  upon  the  application  of  a 
stimulus.  It  is  therefore  increased  by  reflex  nerve-force.  The 
stimuli  may  be  mechanical  or  chemical  or  mental ;  thus  the  flow 
of  saliva  is  increased  by  taking  food  into  the  mouth  or  by  irritat- 
ing the  inside  of  the  mouth  by  scratching  or  burning,  or  by  looking 
at  or  smelling  or  even  thinking  about  food. 

In  the  submaxillary  gland  the  chorda  tympani  nerve  is  said  to 
have  a  double  function — to  increase  the  vascularity  of  the  gland 
by  one  portion  of  its  fibres,  and  to  excite  the  secreting  function  by 
another  set  of  fibres,  the  sympathetic  nerves  of  the  gland  acting  as 
the  vaso-constrictors. 

In  the  parotid  the  vaso-dilator  impulse  comes  also  from  the  facial 
nerve  through  the  fifth  by  the  communication  of  the  lesser  petrosal 
nerve.     The  vaso-constrictor  impulse  comes  from  the  sympathetic. 

There  is  found  a  medullary  centre  which  controls  this  function. 

Describe  an  act  of  deglutition. 

Deglutition,  or  swallowing,  is  the  process  by  which  we  convey 
food  from  the  mouth  to  the  stomach,  and  may  be  divided  for  the 
purpose  of  analysis  into  three  actions :  1st.  The  food  after  masti- 


45 


Human  Alimentary  Canal:  n,  a?sophaf;us ;  /),  stomach  ;  c,  cardiac  orifice;  d,  pylorus;  e, 
small  intestine;  /,  biliary  duct ;  ;;,  pancreatic  duct ;  h,  ascending  colon;  /,  transverse 
colon ;  j,  descending  colon  ;  k,  rectum. 


46 


DIGESTION. 


cation  is  pushed  by  the  tongue  against  the  palate,  and  so  forced  on 
toward  the  fauces.  2d.  As  soon  as  the  bolus  enters  the  pharynx  it 
is  pushed  on  by  the  tongue  and  by  the  contraction  of  the  pillars 
of  the  fauces  and  the  constrictors  of  the  pharynx  toward  the 
oesophageal  opening.  The  pharyngeal  vault  is  guarded  from  in- 
vasion by  solid  or  liquid  food  by  the  valve-action  of  the  soft  palate, 
while  the  opening  of  the  glottis  is  protected  by  the  simulta- 
neous intrinsic  muscular  closure  of  the  rima  glottidis  and  by  the 
valve-like  cover  of  the  epiglottis.  When  the  muscles  of  the  fauces 
and  tongue  push  on  the  food-mass,  they  also  draw  up  the  larynx 
and  dilate  the  oesophageal  opening.  3d.  The  oesophagus  grasps  the 
food,  and  a  peristaltic  wave-series  carries  it  rapidly  on  to  the  cardiac 
opening  of  the  stomach.  The  beginning  (1st)  of  the  act  of  swallow- 
ing is  voluntary,  the  remainder  reflex,  and  is  governed  by  centres  in 
the  medulla  oblongata  acting  through  the  cranial  nerves  which  sup- 
ply the  parts.  The  trigeminus,  glosso-pharyngeus,  and  vagus  by 
their  sensory  and  motor  functions  act  both  in  the  capacity  of  affer- 
ent and  efferent  communication  with  the  medullary  centre. 

Fig.  7. 


Free  Surface  of  the  Gastric  Mucous  Membrane,  viewed  from  above,  from  pig's  stomach, 
cardiac  portion,  moderately  magnified. 


Describe  the  structure  and  function  of  the  stomach. 

The  stomach  (Fig.  6)  is  an  organ  which  resembles  in  structure 


DIGESTION. 


47 


the  rest  of  the  intestinal  tract ;  it  is  liollow,  having  a  peritoneal  cov- 
ering antl  a  mucous  membrane  lining,  with  a  muscular  layer  between. 
It  is  in  this  mucous  membrane  that  tlie  special  function  of  the  stom- 
ach lies,  for  here  are  found  glands  which  secrete  the  gastric  juice. 
The  active  peristaltic  motion  churns  the  food  about  after  deglutition, 
and  exposes  it  thoroughly  to  the  action  of  the  digestive  agents.  The 
function  of  the  stomach  is  the  digestion  of  proteids. 


Describe  the  glands  of  the  stomach. 

If  one  looks  closely  at  the  mucous  surface  of  the  stomach,  it 
is  seen  to  present  a  sort  of  reticulated  (Fig.  7)  appearance, 
meshes  being  larger  at  the  pyloric  than  at  the  cardiac  end  of 
stomach.     It  is  in  the  interstices 


the 
the 


of  this  mesh  that  the  glands 
open.  The  openings  are  smaller 
at  the  cardiac  than  at  the  pyloric 
end,  and  the  character  of  the 
glands  changes :  we  therefore 
speak  of  two  varieties  of  gastric 
glands — 1,  peptic;  2,  pyloric. 

1.  The  peptic  glands  are  ar- 
ranged in  groups  throughout  the 
stomach,  but  not  so  abundantly 
at  the  pyloric  end.  They  often 
consist  of  a  simple  tube  dipping 
into  the  surface  and  lined  with 
columnar  epithelium  (Fig.  8),  but 
they  may  be  branched — i.  e.  sev- 
eral glands  may  empty  into  a 
common  duct.  The  columnar  epi- 
thelium in  the  deeper  portion  of 
the  gland  contains  large,  almost 
globular,  cells,  which  are  known 
as  peptic  cells. 

2.  The  pyloric  glands,  or  mu- 
cous glands,  like  tlie  peptic,  may 
be  simple  or  compound.  The 
ducts  are  larger,  and  the  large 
cells  are  wanting  (Fig.  9).  Dur- 
ing digestion  the  cells  of  both 
varieties  of  glands  become  swoU- 


Fjg 


Compound  Gastric  Follicle,  I'roin  the  car- 
diac portion  of  the  liuniaii  stomach:  1, 
excretory  tiihes  leadin};  to  the  surface; 
2,  tubercular  follicles  containing  sphe- 
roidal cells  (Kiilliker). 


48 


DIGESTION. 


en,  and  in  them  are  found  granules  wliicli  are  supposed  to  be  pepsin 
or  that  from  which  pepsin  is  formed. 

Fig.  9 


Tubular  Follicles,  from  pyloric  portion  of  pig's  stomach,  showing  their  caecal  extremities 
and  epithelial  lining :  at  a  the  torn  end  of  a  follicle,  showing  its  cavity  more  highly 
magnified. 

What  is  the  gastric  juice  ? 

When  the  stomach  is  not  at  work  it  contain-s  no  gastric  juice, 
but  is  bathed  in  an  alkaline  mucus.  As  soon  as  food  enters  the 
organ,  however,  it  immediately  begins  to  secrete  considerable  quan- 
tities of  an  acid  fluid  which  soaks  into  and  mingles  with  the  food. 
The  celebrated  case  of  Alexis  St.  Martin,  who  had  a  gunshot  wound 
resulting  in  gastric  fistula,  enabled  Beaumont,  surgeon  U.  S.  A.,  to 
investigate  accurately  its  composition.  It  is  a  limpid,  colorless  fluid 
of  sp.  gr.  1001-1010  and  acid  reaction.  It  contains  about  i  per  cent, 
solid  matter.     Its  composition  is  nearly — 

Water 99.50 

Pepsin 25 

Hydrochloric  acid 05 

Salts  (alkaline  chlorides  and  phosphates)   .    .        .20 

100.00 

This  composition  is  not  constant,  as  the  proportions  vary  consider- 
ably, HCl,  for  example,  being  present  much  more  abundantly  in 
some  cases. 


DIGESTION.  49 

What  is  the  daily  secretion  of  gastric  juice  ? 
I'min  10  to  20  pints. 

What  is  the  source  of  the  hydrochloric  acid? 

It  is  probably  secreted  by  tlie  cubical  parietal  cells  of  the  peptic 
alamls.      A^er}^  little  seems  to  be  formed  liy  tbe  pyloric  glands. 

What  other  acids  are  found  in  the  stomach? 

Lactic,  acetic,  butyric,  and  some  other  fatty  acids.  They  are 
products  of  digestion  or  of  abnormal  processes  due  to  decomposition 
of  food. 

What  is  the  source  of  pepsin? 

The  globular  cells  in  the  peptic  glands.  These  cells  are  supposed 
to  form  a  substance  called  pejisinoc/en,  from  which  pepsin  is  derived. 
Pepsin  is  derived  for  commercial  or  for  experimental  purposes  from 
fresh  stomachs  by  scraping  the  surface  and  dissolving  out  the  fer- 
ment with  cold  water,  or  by  mincing  the  mucous  membrane  and 
extracting  the  ferment  with  glycerin  after  dehydrating  with 
alcohol. 

What  is  the  function  of  gastric  juice  ? 

The  principal  function  of  the  gastric  juice  is  the  transforming 
of  proteids  into  peptones.  This  action  depends  upon  the  presence 
of  both  pepsin  and  acid.  The  first  change  which  occurs  is  the  foi'- 
mation  of  acid  albumin,  but  as  the  action  of  the  ferment  continues 
the  acid  albumin  is  transformed  to  peptone.  The  presence  of  acid 
albumin  is  demonstrated  by  the  addition  of  an  alkali,  which  precip- 
itates it. 

What  are  the  characteristics  of  peptone? 

(1)  They  are  diftusible— <'.  c.  have  the  property  of  osmosis,  or 
passing  through  an  animal  membrane.  This  is  of  great  importance 
in  digestion,  for  if  this  property  were  absent  no  animal  food  could 
be  absorbed  from  the  intestines.  (2)  They  are  very  freely  soluble 
in  water  and  neutral  solutions.  (3)  They  do  not  respond  to  the 
chemical  tests  for  other  proteid  substances.  They  are  not  precip- 
itated by  heat  and  the  mineral  acids,  but  arc  precipitated  by  tannic 
acid,  picric  acid,  or  by  the  bichloride  of  mercury. 

What  is  the  name  given  the  food  after  digestion  in  the  stomach  ? 
Chyme.     The  action  of  the  pepsin  in  converting  proteids  to  pep- 
tones is  called  a  protcolijtic  action,  and  chemically  its  action  is  to 
cause  a  hydration  of  the  proteid  molecules. 
4— Phy. 


50  DIGESTION. 

What  forms  of  peptones  occur  ? 

(1)  Parapeptone, — acid  albumin,  which  results  from  incomplete 
action  of  the  gastric  juice ;  (2)  antipeptone. — a  form  on  which 
pancreatic  digestion  has  no  effect;  (3)  hemipeptone, — a  form  in 
which  pancreatic  digestion  has  the  effect  of  producing  leucin  and 
tyrosin. 

What  conditions  favor  gastric  digestion? 

The  temperature  of  the  body  is  most  favorable,  and  the  presence 
of  acid — preferably  HCl — ^is  essential.  Digestive  secretion  does 
not  continue  except  during  the  presence  of  food. 

What  is  the  milk-curdling  ferment? 

Milk  is  curdled  in  the  stomach  by  a  ferment,  aside  from  pepsin, 
which  is  derived  from  the  gastric  juice.  This  action  takes  place  in 
the  absence  of  hydrochloric  acid.  Rennet  (derived  from  the  fourth 
stomach  of  calves)  is  used  for  this  purpose  in  the  cheese  manu- 
facture. 

How  are  non-nitrogenous  bodies  affected  by  the  gastric  juice  ? 

Starches  are  unaffected.  Sugar  is  dissolved  and  cane-sugar  (sac- 
charose) is  changed  to  grape-sugar  (glucose)  by  the  aid  of  the  mu- 
cus present.  Fats  are  unaffected,  except  that  the  albuminous  cap- 
sules of  fat-cells  in  adipose  tissues  are  digested  and-  the  oil  set  free 
in  globules. 

What  is  the  time  required  for  the  stomach  digestion? 

The  time  varies,  with  the  kind  and  amount  of  food,  from  one 
to  five  or  six  hours.  Digestion  is  favored  by  rest  of  the  stomach 
before  eating,  by  gentle  exercise  of  the  mind  or  body,  by  an  undis- 
turbed mental  condition,  and  by  a  healthy  condition  of  the  body. 

Does  absorption  take  place  from  the  stomach? 

No,  except  in  a  very  slight  degree. 

How  does  the  stomach  empty  itself? 

The  stomach  is  elastic,  and  is  supplied  with  circular  and  longi- 
tudinal muscles  in  its  middle  coat.  These  muscular  fibres  are 
capable  of  producing  peristaltic  movements  of  the  organ  which  turn 
the  food  over  and  over  during  the  process  of  digestion.  This  elas- 
tic pouch  is  closed  at  each  end  by  strong,  sphincter-like  circular 
bands  of  muscle  at  the  cardiac  and  pyloric  openings,  and  until  the 
stomach  digestion  is  well  advanced  none  of  the  contents  escapes; 


DIGESTION.  51 

but  as  the  peptone-making  advances  tlic  pyloric  opening  permits 
the  escape  of  chyme,  and  tlii.s  is  aided  by  strong  peristaltic  efforts 
on  the  part  of  the  stomach  at  its  pyloric  end.  Toward  the  end  of 
digestion  the  pylorus  permits  the  escape  of  undigested  as  well  as 
of  digested  matter.  The  circulation  of  the  stomach  contents  is  cir- 
cnmferentially  toward  the  pylorus,  but  centrally  toward  the  cardiac 
opening. 

What  is  the  capacity  of  the  stomach  ? 

About  a  quart  in  the  adult,  but  its  muscular  walls  enable  it  to 
contract  so  as  to  fit  its  contents  if  much  or  little. 

What  is  the  nervous  mechanism  of  stomach  digestion  ? 

The  pneumogastric  and  sympathetic  (splanchnic  from  solar 
plexus)  are  the  nerves  which  supply  the  stomach,  and  besides  these 
there  are  numerous  ganglia  in  the  stomach-walls.  The  ordinary 
motion-stimulus  of  the  organ  lies  in  the  intrinsic  ganglia.  Irri- 
tation of  the  pneumogastric  nerve  causes  contraction  ;  its  division, 
cessation  of  peristalsis.  But,  further  than  this,  the  vagus  has  con- 
trol to  considerable  degree  over  secretion  in  the  stomach. 

Describe  vomiting. 

The  regurgitation  of  food  from  the  stomach  through  the  cardiac 
orifice,  and  thence  through  the  mouth,  may  occur  when  the  cardiac 
opening  is  free  and  the  pylorus  is  closed.  This  is  usually  a  reflex 
act,  and  is  performed  by  the  contraction  of  the  stomach,  aided  by 
the  pressure  of  the  abdominal  muscles  opposing  the  fixed  diaphragm. 
It  may  be  described  as  a  reversed  peristalsis.  The  stimuli  which 
excite  the  reflex  may  be  either  local  in  the  stomach  or  peripheral. 
Violent  irritation  of  the  gastric  mucous  membrane  will  excite  it ; 
also  mental  impulses,  from  ocular,  auditory,  or  olfactory  sources ; 
injury  or  irritation  of  the  testis,  ovary,  kidney,  etc.;  unusual 
motion,  as  swinging;  certain  diseases;  and  eff"ort  of  will  in  some 
is  sufficient. 

How  is  this  reflex  controlled? 

By  a  centre  in  the  medulla  oblongata  acting  through  the  pneu- 
nuigastric  nerve. 

What  is  meant  by  rumination  in  man? 

Some  few  persons  have  the  ability  to  force  half-digested  food 
back  from  the  stomach  into  the  mouth,  remasticate  it,  and  again 
swallow  it. 


52  DIGESTION. 

What  do  we  mean  by  "intestinal  digestion"? 

Soon  after  passing  the  pylorus,  food  comes  in  contact  with  the 
alkaline  secretions  of  the  small  intestine  and  of  the  liver  and  pan- 
creas. In  the  small  intestine  the  food  is  still  further  prepared  for 
absorption,  and  from  this  part  of  the  alimentary  tract  the  digested 
food  is  taken  up  for  body  nutrition. 

Describe  the  process  of  digestion  in  the  small  intestine. 

By  the  peristaltic  action  of  the  gut  the  food  is  carried  on  through 
the  length  of  the  organ,  but  its  progress  is  more  or  less  impeded 
by  the  valvulas  conniventes.  These  folds  of  the  mucous  coat  not 
only  retard  the  too  rapid  advance  of  food,  but  cause  it  to  be  thor- 
oughly exposed  to  the  action  of  the  digestive  fluids. 

How  is  the  peristaltic  action  regulated? 

By  the  sympathetic  system  of  nerves.  Auerbach's  plexus  lies 
between  the  circular  and  longitudinal  muscular  coats.  It  is  also 
known  as  the  plexus  mesentericus. 

How  is  the  blood-supply  regulated? 

Also  by  the  sympathetic  system.  Meissner's  plexus  lies  beneath 
the  mucous  coat,  and  is  regarded  as  the  source  of  control  of  the 
blood-supply  and  of  the  function  of  absorption. 

What  are  the  glands  peculiar  to  the  small  intestine  ? 
Lieberkiihn's,  Brunner's,  and  Peyer's  glands. 

Describe  Lieberkiihn's  glands. 

These  glands  (or  follicles  or  crypts)  are  thickly  distributed  over 
the  whole  surface  of  the  small  and  large  intestine,  being  larger  in 
the  large  intestine.  They  are  simply  tubular  depressions  in  the 
mucous  membrane,  lined  with  columnar  epithelium,  which  contains 
occasional  large  "  goblet  "-cells. 

What  are  Brunner's  glands? 

They  are  found  in  the  duodenum  alone,  and  are  situated  in  the 
submucous  tissue.  They  resemble  the  pyloric  glands  of  the  stom- 
ach, and,  like  them,  are  usually  compound  glands.  The  duct  of 
the  gland  passes  up  through  the  mucous  membrane  and  opens  at 
its  surface. 

What  are  Peyer's  glands? 

These  are  of  two  varieties  :  (1)  solitary  ;  (2)  agminate. 


DIGESTION.  53 

(1)  Solitary  glands  consist  of  a  rounded  mass  of  whitish  adenoid 
tissue  about  tj'-  to  y'^  in.  in  diameter,  situated  in  the  submucous 
tissue,  but  often  projeetinj^-  to  tlie  surface  of  the  intestine.  Eacli 
lymphoid  mass  is  surrounded  by  Lieberkiilm's  iullicles. 

('Z)  Afi'uiinate  glands  (Peyer's  patches)  consist  of  groups  of  these 
adenoid  masses,  making  "patches  "  in  the  mucous  membrane  2  to  3 
in.  long  and  about  2  in.  wide. 

What  is  the  function  of  the  intestinal  glands  ? 

Secretion  of  the  intestinal  juice  (succus  cntericus). 

What  is  the  function  of  the  intestinal  juice  ? 

Its  etfect  upon  digestion  is  not  fully  understood,  but  it  probably 
has  some  effect  upon  saccharose,  and  possibly  upon  proteids,  con- 
verting the  one  into  glucose  and  the  other  into  peptones.  However, 
its  chief  function  seems  to  be  to  supply  the  loss  of  fluid  to  take 
the  place  of  that  which  is  absorbed  as  digestion  progresses.  At 
any  rate,  the  contents  of  the  small  intestine  as  they  enter  the  colon 
are  about  as  fluid  as  when  they  leave  the  stomach. 

What  other  glands  discharge  their  secretions  into  the  small  in- 
testine ? 
The  pancreas  and  the  liver. 

Describe  the  pancreas. 

The  pancreas  is  an  organ  lying  in  the  upper  part  of  the  abdo- 
men in  contact  with  the  duodenum  :  in  length  it  is  about  6  in.,  and 
is  thicker  at  its  right  or  duodenal  end.  It  is  a  conglomerate  gland, 
resembling  in  structure  the  salivary  glands.  During  digestion  it  is 
active,  but  is  quiescent  in  the  intervals.  Its  secretion,  pancreatic 
fluid,  is  discharged  into  a  main  duct  which  receives  branches  from 
the  lobes  of  the  gland,  and  is  emptied  with  the  bile  through  a  com- 
mon opening  about  2  or  3  in.  beyond  the  pylorus.  During  digestion 
the  cells  of  the  organ  become  granular,  and  the  granules  are  thought 
to  consist  of  the  substance  from  which  the  ferments  of  the  pancreas 
are  derived,  zijiuogcii,  rather  than  of  the  ferments  themselves. 

What  are  the  characteristics  of  pancreatic  secretion  ? 

The  pancreatic  juice  is  a  clear,  colorless  fluid,  having  an  alkaline 
reaction  and  a  notably  viscid  consistency.  It  coagulates  with  heat, 
and  is  made  quite  gelatinous  by  cold.  Specific  gravity,  1015.  Its 
composition  varies,  but  in  general  is  as  follows : 


9 


54  DIGESTION. 

Water 90 

Organic  matter : 

Ferments, 

Serum  albumin 

Alkali  albumin 

Fats,  soaps,  etc.,  j 
Inorganic  salts  (chiefly  sodium  carbonate)  ...       1 

~100 
What  are  the  pancreatic  ferments? 

(1)  Trypsin,  a  peptone-forming  (proteolytic)  ferment,  which, 
continues  the  digestion  of  proteids  begun  in  the  stomach.  It 
forms  a  peptone  which  resembles  the  stomach  .peptone  in  its 
reactions.  This  ferment,  unlike  pepsin,  only  acts  in  an  alkaline 
medium.  It  acts  less  vigorously  upon  gelatins  and  other  nitrog- 
enous bodies. 

(2)  Amylopsin,  a  starch-changing  (amylolytic)  ferment,  by 
which  starch  is  converted  to  maltose,  and  finally  glucose,  as  by 
the  ptyalin  in  the  saliva. 

(3)  (unnamed),  a  rennet  or  milk-curdling  ferment.    This 

ferment  will  act  in  the  presence  of  an  acid. 

(4)  Strypsin  (?),  a  questionable  ferment  by  which  fats  are 
broken  up  from  the  large  globules  and  emulsified  or  saponified 
in  alkaline  media.  It  is  claimed  by  some  that  this  is  not  a  fer- 
ment action,  but  is  the  result  of  the  action  of  the  alkaline  intes- 
tinal contents  upon  the  fat. 

Of  these  processes  the  emulsification,  or  breaking  the  fat-glob- 
ules into  minute  particles,  is  by  far  the  more  important,  as  it 
allows  this  form  of  food  to  be  absorbed  from  the  gut.  Milk  is 
an  excellent  example  of  a  natural  emulsion. 

Saponification  (or  soap-making)  results  from  the  fatty  acid 
combining  with  an  alkah,  forming  the  corresponding  salt  and 
glycerin — e.  g.  : 

stearin  +  Potassium  Hydrate  =     Potassium  Stearate     +  Glycerin. 

^  CsHf^^'  j  O3  +      3  1 1  0      =3  (g«H350  )  Q^  ^  C3H5 1  Q^ 

What  is  the  function  of  the  pancreatic  juice  ? 

It  is  most  active  in  the  digestion,  and  is  peculiar  in  having  an 
effect  upon  all  forms  of  food  which  require  preparation  for  absorp- 
tion — upon  proteids,  starches,  and  fats,  as  well  as  upon  milk. 


DIGESTION.  55 

What  conditions  favor  the  action  of  the  pancreatic  fluid  ? 

Moderate  heat  (1UU°  ¥.),  an  alkaline  medium,  and  the  removal 
of  the  products  of  the  ferment-action  as  soon  as  the  change  is 
completed. 

What  name  is  given  to  the  intestinal  contents  of  the  pancreatic 
digestion  ? 

Chyle. 

Describe  the  liver. 

The  liver  is  the  largest  gland  in  the  body,  and  is  situated  in  the 
upper  part  of  the  abdominal  eavity.  It  secretes  a  fluid  known  as 
the  bile  or  gall,  which  is  stored  in  a  bladder  lying  attached  to  its 
lower  surface.  The  functions  of  the  organ  are — (1)  secretion,  and 
(2)  the  elaboration  of  the  blood. 

What  is  the  character  of  bile  ? 

It  is  a  viscid,  almost  ropy  fluid,  of  a  yellow  or  red  or  greenish 
color  and  bitter  taste.  It  is  fi\intly  alkaline  or  neutral  in  reaction, 
and  has  a  specific  gravity  of  about  1020.  Its  composition  is, 
approximately — 

Water 86 

r  Bile  salts,  9  ^ 

Organic  matter,  -j  Fat  and  cholesterin,    1  v     ....     13 

(  Mucus  and  pigments,  3  ) 
Inorganic  salts 1 

100 
How  is  the  flow  of  bile  excited  ? 

The  secretion  of  the  liver  is  stored  in  the  gall-bladder  until  its 
flow  is  excited  by  the  acid  discharge  of  the  stomach-contents  into 
the  duodenum.  It  is  an  active  secretion,  and  not  a  passive  filtra- 
tion from  the  blood,  for  if  a  manometer-tube  be  listened  in  the 
duct  it  will  indicate  a  pressure  greater  than  that  of  the  blood. 
"While  tlie  gall-bladder  acts  as  a  storage  reservoir,  the  bile  does  not 
necessarily  enter  it,  but  may  discharge  directly  from  the  hepatic 
into  the  common  duct.  The  opening  of  the  common  duct  into  the 
duodenum  is  guai'ded  by  a  sphincter-like  aiTangement  of  the  muscu- 
lar fibres  in  the  gut-wall.  The  gall-bladder  and  the  gall-duct  are 
])rovided  with  unstriped  muscular  fibres,  so  that  they  may  empty 
themselves.  Inspiration  and  expiration  bring  alternating  pressure 
upon  the  gall-bladder,  and  aid  in  emptying  it. 


56 


DIGESTION. 


What  is  the  quantity  of  bile  secreted  daily  ? 

The  quantity  varies  with  the  amount  of  food  taken,  but  is  esti- 
mated to  vary  between  20  and  40  ounces,  or,  approximately,  from 
a  pint  to  a  quart,  in  twenty-four  hours. 

What  is  the  resemblance  between  bile  and  meconium  ? 

There  are  strong  similarities.  Meconium  contains  considerable 
proportions  of  bile  salts  and  pigment,  as  well  as  cholesterin.  It  is 
supposed  that  in  the  foetus  the  liver  has  the  function  of  purifying 
the  circulating  blood  and  excreting  certain  oflfensive  matters  in  this 
way. 

What  are  some  of  the  more  important  ingredients  of  bile  ? 

(1)  Bile  salts,  sodium  glycocholate  and  sodium  taurocholate. 
They  may  be  isolated  in  crystalline  form  from  bile,  and  are  pres- 

FiG.  10. 


Cholesterin  from  the  Contents  of  an  Encysted  Tumor. 

ent  in  human  bile  in  about  equal  proportions.  They  are  soluble 
and  very  deliquescent  colorless  crystals  which  have  the  bitter  taste 
of  bile.  Test  by  Pettenkofer's  method :  Add  to  a  solution  of  bile 
a  small  amount  of  a  solution  of  cane-sugar.  On  treating  this 
solution  with  pure  sulphuric  acid  drop  by  drop  there  is  first  a 
precipitation  of  a  turbid  sediment  (cholic  acid).     This  is  cleared 


DIGESTION.  57 

by  a  further  addition  of  sulphuric  acid,  and  the  solution  assumes 
a  bright  cherry  color,  cluinging  to  violet,  and,  if  much  bile  be 
present,  to  deep  purple. 

(2)  ('cy/o//y/r/ »/a^^'<- of  the  bilo,  biliverdiii  and  bilirubin.  Both 
piirnients  ure  found  in  human  bile,  but  the  former  is  characteristic 
of  the  bile  of  herbivora,  and  the  latter,  bilirubin,  of  the  bile  of 
caniivora.  The  pitrments  are  crystallizablc,  and  are  insoluble  in 
water.  The  crystals  have  the  ureen  and  red  colors  of  the  pij^ments. 
Test,  "  Gmelin's  bile  test:"  Add  fumini;;  nitric  (nitroso-nitric)  acid, 
and  there  results  a  play  of  colors  which  is  best  seen  when  the  bile 
solution  is  in  thin  layer  on  a  white  plate.  The  presence  of  the 
bile-pigments  is  shown  also  by  absorption-bands  in  the  spectrum. 
Bilirubin  is  probably  derived  from  hivmoglobin,  and  biliverdin  from 
the  bilirubin,  as  they  are  chemically  closel}'  allied. 

(8)  Choksfen'i),  a  crystallizablc.  insoluble  substance  which  belongs 
to  the  alcohol  group  in  chemical  composition.  Best  recognized  by 
microscopic  appearance  of  ci'ystals  (Fig.  10),  though  it  may  be 
tested  chemically  by  the  addition  of  sulphuric  acid,  which  gives  a 
red  reaction. 

What  are  the  functions  of  the  liver  ? 

This  must  be  considered  to  be  still  a  somewhat  unfinished  prob- 
lem, but  we  can  safely  assume  three  duties  :  (1)  that  of  excretion, 
(2)  as  an  element  in  the  process  of  digestion,  (3)  the  elaboration  of 
absorbed  food  before  passing  it  into  the  blood-circulation.  Of  the.se 
uses,  (1)  and  (2)  are  dependent  upon  the  secretion  of  bile  ;  (3)  is  an 
intrinsic  property  of  the  organ. 

What  excretory  function  has  the  liver? 

The  bile  for  the  most  part,  in  normal  conditions,  is  a  sort  of  circu- 
lating fluid  :  it  is  secreted  by  the  liver,  poured  into  the  intestines, 
and  reabsorbed  from  them,  to  be  returned  through  the  portal  vein 
to  the  liver  for  recirculation.  There  is,  however,  a  small  propor- 
tion of  biliary  matter,  about  one-sixteenth,  which  is  not  absorbed, 
and  this  consists  chiefly  of  the  pigments  of  the  bile.  The  salts 
are  nearly  all  reabsorbed  in  the  assimilation.  Further  than  this, 
the  liver  is  found  to,  so  to  speak,  filter  materials  which  would 
be  poi.sonous  if  circulating  in  the  general  system,  and  either  to 
reject  them  at  once  or  to  store  them  up  and  reject  them  slowly- 
back  to  the  intestine.  The  excrementitious  material  from  the  liver 
is  known  as  stercobilin.  Stercorin  is  found  in  the  fjvces,  and  is 
thought  to  be  an  excretion  of  the  liver:  it  closely  resembles  cho- 


58  DIGESTION. 

lesterin,  and  is  supposed  to  be  a  modification  of  cholesterin  by 
digestion.  Whether  or  not  the  stercorin  (cholesterin)  is  an  excre- 
tion of  the  liver  corresponding  to  the  urea  of  the  kidney  is  some- 
what uncertain. 

What  effect  has  bile  upon  the  digestion? 

(1)  The  alkaline  reaction  of  the  bile  aids  the  pancreatic  and  checks 
the  pepsin  digestion  ;  it  aids  in  the  emulsion  of  the  fats,  and  is 
probably  very  active  in  this  process.  (2)  It  moistens  the  mucous 
membrane  and  favors  the  absorption  of  digested  food.  (3)  It  acts 
as  a  natural  purgative  and  as  a  natural  antiseptic,  and  in  this  way 
is  very  essential  to  the  proper  performance  of  the  digestive  process. 
As  a  purgative  bile  acts  by  stimulating  peristalsis. 

What  is  the  effect  of  the  liver  upon  absorbed  chyle  ? 

(1)  Peptones  resulting  from  the  digestion  of  proteids  undergo 
some  modification  in  the  liver,  for  it  is  found  that  if  injected  into 
the  portal  vein  they  do  not  appear  in  the  urine,  while  if  injected  into 
the  general  system  they  do  appear.  This  matter  is  not  fully  under- 
stood as  yet,  since  the  change  the  peptones  undergo  in  the  lym- 
phatic vessels,  to  allow  absorption  without  relation  to  the  liver,  is 
still  in  the  dark. 

(2)  The  liver  normally  forms  a  substance  resembling  starch  in  its 
chemical  composition.  This  is  known  as  glycogen,  and  is  formed 
from  glucose  taken  up  by  the  portal  circulation.  Its  chemical  for- 
mula is  that  of  starch  (CgHigOs),  and  it  is  derived  from  glucose 
(CgHijOe)  by  dehydration,  and  is  rapidly  changed  by  diastatic  fer- 
ments to  glucose.  This  process  is  known  as  the  glycogenic  function 
of  the  liver :  its  use  is  supposed  to  be  the  storage  of  a  fund  of 
carbohydrate  material  (an  "  animal  starch  ")  to  maintain  a  steady 
supply  to  the  system. 

What  is  the  duty  of  the  large  intestine  in  digestion  ? 

The  chyme  which  enters  the  large  intestine  still  continues  in  the 
influence  of  the  ferments,  and  the  process  of  digestion  continues. 
The  food  may  undergo  acid  fermentation  here,  but  there  is  no  new 
digestive  action.  That  the  large  intestine  may  have  the  power  of 
acting  upon  food  is  shown  by  the  absorption  of  fats,  proteids,  etc. 
which  are  taken  in  nutrient  enemata. 

Describe  defecation. 

The  expulsion  of  the  refuse  of  digestion  from  the  intestine  is 
partly  a  voluntary  act,  but  more  especially  reflex.     The  voluntary 


ABSORPTION.  59 

act  is  the  pressure  of  the  abdoiuiiial  muscles  upon  the  contained 
viscera,  wliile  the  reflex  is  an  increased  j)eristalsis  in  the  sigmoid 
flexure  and  rectum  and  tlie  rehixation  of  the  spliincter.  The  centre 
which  governs  tliis  act,  so  far  as  it  is  reflex,  lies  in  the  lumbar 
region  of  the  spinal  cord. 

ABSORPTION. 

What  is  absorption? 

The  digested  food  is  taken  from  the  intestines  and  carried  into 
the  l)lood,  whence  it  is  taken  to  nourish  the  cells.  This  process 
we  know  as  absorption.  The  same  term  is  applied  to  the  removal 
of  worn-out  material  from  the  tissues. 

By  what  channels  is  food  absorbed  from  the  intestines? 

By  the  ]>loi id- vessels  and  lymphatics. 

What  property  of  chyle  renders  it  fit  for  absorption  ? 

The  property  of  passing  through  animal  membranes.  Chyle  is 
the  name  given  to  food  after  digestion.  By  digestion  the  proteids, 
starches,  and  fats,  which  were  not  dialj'zable.  have  become  pep- 
tones, sugars,  and  emulsified  fat.  All  these  products  of  digestion 
are  readily  capable  of  dialysis,  and  therefore  ready  for  absorption. 

What  is  dialysis? 

By  dialysis  we  mean  the  property  of  fluids  which  enables  them 
to  pass  through  animal  membranes — osmosis.  This  we  have  seen 
is  possessed  in  a  high  degree  by  the  ingredients  of  chyle.  The 
reverse  process  may  occur,  and  fluids  (serum)  from  the  blood  may 
similarly  be  drawn  into  the  intestinal  canal,  as  is  seen  when  the 
salines  are  used  as  purgatives. 

What  anatomical  features  of  the  gut  favor  absorption  ? 

(1)  The  valvulai  conniventcs  greatly  increase  the  area  of  the 
intestinal  surface,  and  by  their  shelf-like  formation  delay  the  ad- 
vance of  ch3'le.  (2)  The  villi  of  the  intestine  not  only  increase 
the  area,  but  are  the  .special  organs  of  the  function  of  absorption. 
(3)  The  contraction  of  the  intestine  upon  its  fluid  contents  also 
favors,  mechanically,  the  filtration  of  the  contents  through  its  walls. 

What  are  the  villi? 

The  villi  are  almost  innumerable,  minute,  teat-like  projections 
from  the  surface  of  the  wall  of  the  intestine.  They  are  very 
numerous  in  the  small  intestine,  and  none  are  found  in  the  largo 


60 


ABSOEPTION. 


gut.     Each  villus  is  covered  by  an  epithelial  layer,  and  within,  sup- 
ported by  areolar  tissue,  is  a  delicate  capillary  network  of  blood- 

FlG.  11. 


Fig.  12. 


I^ 


Fig.  U. — An  Intestinal  Villus :  a,  layer  of  cylindrical  epithelium,  with  its  external  trans- 
parent striated  portion;  hb,  blood-vessels  entering  and  leaving  the  villus;  c,  lym- 
phatic vessels,  occupying  its  central  axis  (Leydig). 

Fig.  12. — Patch  of  Peyer's  Glands,  from  the  lower  part  of  the  ileum,  shovping  villi  (mag- 
nified). 

vessels,  a  muscular  layer  (muscularis  mucosae),  and  a  more  or  less 
branched  ending  of  a  lacteal  vessel  (Figs.  11  and  12).  The  ileo- 
caecal  valve  shows  the  absolute  alteration  which  is  apparent  in  the 
mucous  membrane  of  the  small  as  compared  with  the  large  intes- 
tine. On  the  side  toward  the  ileum  are  found  villi  in  great  num- 
bers, while  its  cgecal  side  shows  none. 

Where  does  the  absorption  occur  in  the  intestine? 

Probably  throughout  its  length  in  some  degree.  In  the  stomach 
and  large  intestine  the  absorption  is  very  much  less  than  in  the 
small  intestine,  but  there  is  reason  to  think  that  there  is  consider- 
able activity  of  absorption  from  the  entire  gut  so  long  as  digestion 
continues. 


ABSORPTION. 


61 


What  becomes  of  the  food  absorbed  by  the  blood-vessels  ? 

It   is   taken    by  the  portal   vein   to  tlic  liver,  and  tiicrc  further 
elaborated  for  tissue-nutrition. 

What  becomes  of  the  food  absorbed  by  the  lacteals  ? 

It  is  colK'clt'd  rmni  all  llu;  Ivnipli-spaces  in  tin;  villi  and  about  the 
jzlandular  structure  of  tlie  intestines,  and  is  taken  thence  into  the 
larger  lacteals,  whence  it  passes  through  the  mesenteric  lymphatic 
glands  and  into  the  receptaculum  chyli  of  the  thoracic  duct  (Fig.  13). 
Hence  it  passes  on  into  the  blood-vas- 
cularsystem,  which  it  joins  at  the  root 
of  the  neck  at  the  union  of  the  left  in- 
ternal jugular  and  subclavian  veins. 

Does  chyle  undergo  change  in  the 
lacteals  ? 

Yes.  Peptones,  as  such,  are  not 
found  in  the  blood  nor  in  the  thoracic 
duct,  and  in  the  same  way  sugar  is 
not  more  abundant  in  chyle  after 
absorption  than  in  the  blood ;  nor 
can  we  fully  account  for  the  fats 
which  are  absorbed.  The  trace  is 
lost,  to  a  great  degree,  after  absorp- 
tion of  most  substances,  and  we  do 
not  know  the  exact  history  of  the 
metamorphoses  which  render  them 
fit  for  tissue-building. 

What  elements  are  chiefly  taken 
up  by  the  portal  system? 
All  elements  to  a  greater  or  less 
degree,  but  the  crystallizable  sub- 
stances are  taken  up  in  greater  pro- 
portion by  the  blood-vessels  than  by 
the  lacteals.  Thus  we  find  that 
sugars  and  salts  seem  to  pass  into 
the  portal  system,  and  the  proteids  

and  fats  into    the  lacteal  system  in  a    I.acteals  and  Lymphatics  during  Di- 

little  greater  proportion.  ^^*  ""*' 

What  is  the  appearance  of  chyle  in  the  lacteals? 

It  is  opacjue,  whitish,  milky  from  the  minute  fat-globules  which 


62  ANIMAL   HEAT. 

are  suspended  in  it  (emulsion).  The  basis  of  the  fluid  found  in 
the  lacteals  is  lymph,  and  it  is  only  during  digestion  that  the  lymph 
in  the  visceral  lacteals  becomes  chylous. 

What  is  the  character  of  lymph  ? 

It  is  a  limpid,  watery  fluid,  which  differs  from  blood-plasma  only 
in  that  it  is  somewhat  more  watery.  Like  plasma,  the  lymph  co- 
agulates or  clots  on  exposure  to  the  air,  but  the  clot  is  not  so  firm, 
and  the  clotting  is  due  to  the  presence  of  fibrinogen  and  globulin. 
Chyle  is  lymph  in  which  there  is  present  an  increased  amount  of 
fatty  and  proteid  material. 

What  conditions  favor  the  absorption  of  food  ? 

To  be  absorbed  by  the  blood-vessels  or  lacteals  we  must  have 
substances  in  (1)  a  fluid  state,  and  the  more  dilute  in  solution  the 
more  ready  the  absorption  ;  insoluble  substances  are  not  apprecia- 
bly aff"ected  by  this  process,  nor  are  any  dense  solutions  readily 
taken  up.  (2)  The  rapid  removal  of  the  absorbed  matter  and  the 
renewal  of  fresh  blood  in  the  capillaries  is  of  importance.  Thus, 
if  the  portal  circulation  is  obstructed,  so  that  the  blood  is  circulat- 
ing slowly  or  the  capillaries  are  tense  from  intravascular  pressure, 
the  absorption  will  be  slow. 

What  is  the  quantity  of  chyle  which  is  taken  into  the  system 
daily  ? 
This  is  somewhat  problematical,  but  it  is  estimated  to  be  about 
one-half  to  two-thirds  of  the  volume  of  the  blood. 

How  is  lymph  propelled  in  the  lymphatic  vessels  ? 

In  the  villi  are  bands  of  unstriped  muscle  (musculi  mucosae), 
which  act  to  propel  it  into  the  larger  channels  ;  muscular  pi-essure 
upon  the  lymph-vessels  and  intrinsic  contractile  power  of  the  vessel- 
walls  help  it  along ;  while  the  pumping  force  of  the  respiratory 
movements  and  the  "  negative  pressure  "  in  the  great  veins  are  of 
great  value  in  maintaining  the  circulation. 

ANIMAL  HEAT. 
What  is  the  normal  temperature  of  the  body  ? 

98.5°  F.  (37°  C).  This  temperature  is  not  invariable,  but  in 
the  superficial  cavities,  mouth,  and  axilla,  which  are  convenient  for 
ascertaining  the  body-temperature,  this  is  nearly  exact.     In  the  in- 


ANIMAL   HEAT.  03 

ternal  organs  the  theriiioinotcr  may  indicate  as  liigh  as  100°  F.  in 
normal  conJitions.  In  the  rectum  the  temperature  is  about  1°  F. 
liighcr  than  in  mouth  or  armpit. 

Is  this  normal  temperature  constantly  maintained? 

Yes,  with  very  trifling  variations.  I  nder  all  circumstances  the 
healthy  body  maintains  about  this  temperature,  varying  very 
slightly  uiulcr  torrid  and  frigid  climates.  There  are  also  slight 
variations  from  exercise,  age,  etc. 

How  is  this  heat  maintained? 

It  is  produced  from  union  of  the  oxygen  of  the  air,  which  is 
taken  up  by  the  blood  in  the  lungs,  with  carbon  and  hydrogen. 
This  is  an  exact  analogy  of  combustion  in  the  air. 

What  products  result  from  this  combustion  in  the  body  ? 

Carbonic  oxide  and  water. 

What  is  metabolism? 

It  is  a  change  constantly  going  on  in  the  body  by  which  the 
protoplasm  of  cells  is  destroyed  in  doing  work  (destructive  metab- 
olism), and  by  which  new  protoplasm  is  built  up  by  the  assimi- 
lation of  food  (constructive  metabolism).  When  any  group  of 
cells  is  in  active  use  {<'.g.  in  a  muscle)  the  destructive  process 
is  rapid  and  the  formation  of  carbonic  oxide  and  water  is  active  ; 
in  other  words,  there  is  active  combustion  of  the  cells  with  the 
production  of  heat.  Simultaneously,  there  is  reconstruction  of 
the  used  protoplasm,  but  this  process  is  not  accompanied  by  the 
creation  of  heat. 

How  is  the  loss  of  heat  regulated  ? 

(1)  The  blood  at  the  surface  of  the  body  is  cooled  by  the  colder 
air  or  by  evaporation  of  the  sweat.  This  is  automatically  regulated 
by  the  vaso-motor  nerves,  for  upon  exposure  to  a  colder  atmosphere 
there  is  immediate  contraction  of  the  superficial  capillaries,  and  upon 
entering  a  warmer  environment  there  is  dilatation  ;  so  that  the  quan- 
tity of  blood  presented  for  cooling  is  an  inconstant  factor,  depeiuling 
upon  external  temperature.  The  sweat-production  is  similarly  under 
reflex  control. 

(2)  Loss  of  heat  is  considerable  by  the  lungs,  though  less  than 
that  from  the  skin  :  the  air  is  warmer,  in  usual  conditions,  after 
leaving  the  lungs  than  before  it  has  entered  them. 


64  SECRETION. 

(3)  Clothing  and  the  protection  aiforded  by  houses,  and  the  ele- 
vation of  the  temperature  of  air  indoors  by  fire,  are  factors  in  the 
regulation  of  the  body-temperature. 

What  is  meant  by  heat-centres  in  the  brain? 

There  are  reasons  for  believing  that  there  are  nervous  centres 
exciting  the  heat-production  in  the  tissues  (thermogenic  centres), 
and  centres  which  check  the  metabolism  of  tissue,  and  thus  con- 
trol the  temperature  (inhibitory  heat-centres).  ,  This  is  not  entirely 
proven,  nor  can  these  centres  be  localized.  We  do  know  that  the 
innervation  of  a  part  is  necessary  for  the  maintenance  of  its 
warmth,  aside  from  vaso-motor  causes  for  alteration  of  tempera- 
ture. 

What  are  the  extreme  limits  of  body-temperature  found  in  life  ? 

In  ordinary  pathological  conditions  the  temperature  does  not 
remain  long  at  a  point  below  95°  P.  or  above  105°  F.  without 
fatal  results.  Under  extreme  conditions  of  prolonged  exposure  to 
cold  and  the  algid  stage  of  cholera  recovery  has  occurred  after  a 
bodily  temperature  as  low  as  75°  F.  On  the  other  hand,  in  some 
cases  of  extreme  fever,  as  from  sunstroke,  recovery  has  been  noted 
after  a  temperature  of  110°-112°  F.  has  been  observed. 

SECRETION. 

What  are  secretions? 

Materials  separated  from  the  blood  by  the  cells  to  serve  some 
further  purpose  in  the  animal-  economy.  These  secretions  are  for 
the  most  part  elaborated  by  the  glands,  though  the  mucous  and 
serous  membranes  act  in  this  capacity  as  well.  Examples  of 
secretions  are  found  in  milk,  bile,  gastric  juice,  tears,  etc. 

What  are  excretions? 

Materials  which  are  separated  from  the  blood  by  cell-activity 
and  discharged  from  the  body,  being  either  useless  or  harmful  if 
retained  ;  e.  g.  ui'ine,  sweat. 

What  is  the  function  of  the  serous  secretions  ? 

Lubrication  of  surfaces  in  which  friction  is  undesirable.  Such 
conditions  are  found  in  the  pleural  cavity,  peritoneum,  tunica 
vaginalis,  and  in  a  similar  way  in  the  synovial  cavities  of  joints, 
tendon-sheaths,  etc. 


SECRETION. 


65 


What  is  the  function  of  mucus  ? 

To  lubricate  and  inoi.steii  the  soft  and  delicate  cells  of  mucous 
membrane.  Mucous  tracts  which  are  so  protected  are  the  digestive, 
respiratory,  and  genito-uriuary. 

How  are  these  processes  of  secretion  and  excretion  carried  on  ? 

r»y  mean,-  (if  the  activity  of  the  cells.  In  most  cases  the  cells 
are  grouped  in  organs  which  are  known  as  glands.  The  serous 
fluids  are  the  only  notable  exception  to  this  rule,  the  endothelial 
cells  secreting  without  the  intervention  of  complex  anatomical 
groups. 

What  forms  of  secreting  glands  occur? 

1.  Si))ipir  tit/ntivii,  or  tuhnlar  (/hinih,  which  are  pits  or  depres- 
sions in  epithelial  surfaces  lined  with  epithelial  cells.  The  mucous 
surfaces  furnish  the  most  numerous  examples  of  this  form  of 
gland,  follicles  of  Lieberkiihn  (Fig.  14),  tubular  (mucous)  glands 

Fig.  14. 


Follicles  of  Lieberkiihu,  lioiu  small  intestine  of  dog. 

of  the  stomach  ;  but  the  skin,  in  the  sweat-glands,  shows  a  more 
complicated  form  of  tubular  gland  in  that  it  is  convoluted  and 
tortuous. 

2.    Compound  tuhuhir  glanih  consist  of  a  tubular  gland  which 

5— Phy, 


ee 


SECRETION. 


subdivides   the   main    tubule, 


Fig.  15. 


Portion  of  one  of  Bruuner's  Glands,  from 
human  intestine. 


SO  as  to  have  several  branching 
tubules  leading  into  it.  Often 
these  branches  again  subdivide 
so  as  to  form  a  group  of  ulti- 
mate glandular  elements  grouped 
about  the  main  tubule,  which  acts 
as  a  duct.  This  form  of  gland  is 
found  in  kidney,  testis,  salivary 
and  mammary  glands,  Brunner's 
glands  (Fig.  15),  and  in  many  of 
the  other  glandular  structures. 

3.  Racemose  or  aggregate  glands^ 
in  which  the  glandular  structure 
is  divided  into  lobules  or  acini. 
These  glands  may  be  regarded 
as  a  refinement  of  the  compound 
tubular  variety,  and  examples  are 
found  in  the  salivary  glands  and 
in  the  Meibomian  follicles. 

How  is  secretion  effected  by  the  glands  ? 

(1)  By  physical  processes — viz.  filtration  and  dialysis — the  cells 
are  able  to  separate  from  the  blood-plasma  the  ingredients  which 
make  up  the  secretion.  It  is  important  to  remember  that  the  force 
of  dialysis  may  actually  operate  against  pressure,  and  is,  conse- 
quently, not  a  mere  negative  process  ;  and,  again,  the  fact  that  the 
condition  of  the  blood  as  to  consistency  and  saline  ingredients 
makes  filtration  a  sort  of  check-valve  upon  the  permanency  of  the 
blood-condition. 

(2)  By  chemical  processes  the  cells  of  glands  manufacture  new 
substances  not  found  in  the  blood-plasma  and  add  them  to  the 
secretions.  These  processes  are  peculiarly  noticeable  in  the  fer- 
ment-producing glands,  salivary,  peptic,  and  pancreatic. 

What  circumstances  affect  glandular  activity? 

(a)  If  the  amount  of  hlood passing  through  a  gland  be  increased, 
there  will  be  increased  activity  of  the  function,  and,  conversely,  as 
a  rule,  during  functional  activity  the  gland  will  increase  in  vascu- 
larity. The  stomach,  for  example,  during  digestion  is  quite  en- 
gorged, and  when  idle  is  supplied  with  much  less  blood,  as  is  seen 
by  the  color  deepening  during  its  period  of  activity. 

(J))  An  increase  in  the  material  upon  which  the  gland  acts  stimu- 


THE   MAMMARY  GLANDS.  67 

lates  the  gland  to  greater  effort  ami  iiioreases  the  production  of  the 
ghuid.  Thus,  the  amount  <tt'  urea  is  increased  by  an  increase  of 
nitroiicnous  waste,  as  l)y  exercise,  or  by  an  increase  of  nitrogenous 
matter  in  tlie  blood,  as  by  a  full  meal  of  animal  food. 

(f)  The  iirrroiis  s^sto)!  cxois  (Ui  actirr  Injlaence  upon  secretion. 
This  is  usually  reflex  in  character,  and  fre(juently  is  active  through 
the  vaso-motor  nerves,  as  when  the  salivary  and  gastric  secretion.s 
are  increased  by  the  sight  or  smell  of  food,  as  well  as  by  its  actual 
administration.  There  is  also  a  so-called  tropldc  influence  of  the 
nervous  system,  which  directly  affects  the  secreting  power  of  a 
gland :  this  is  especially  well  shown  in  the  case  of  the  chorda 
tympani  in  its  relation  to  the  secretion  of  the  submaxillary 
gland. 

Describe  the  correlation  of  the  secretions. 

There  oi'ten  seems  to  be  a  relation  in  the  amount  of  one  secre- 
tion to  that  of  some  of  the  others ;  thus  in  a  diseased  condition  of 
the  intestinal  mucous  membrane,  with  increased  secretion,  there 
will  often  be  an  increase  of  the  bile  secreted,  and  perhaps  a 
diminution  of  other  secretions,  as  salivary  or  urinary.  And,  again, 
unusual  perspiration  is  followed  by  decrease  in  the  activity  of  the 
kidneys. 

THE  MAMMARY  GLANDS. 
Describe  the  mammary  glands. 

They  are  large  glands  which  are  made  up  of  several  distinct 
lobes.  f]ach  lobe  has  its  duct,  which  leads  to  the  nipple,  and 
there  are  about  twenty  such  lobes  and  ducts.  The  lobes  are 
subdivided,  and  the  small  lobes,  lobules,  or  alveoli  are  made  up 
of  the  terminal  tubules  of  the  duct,  which  lie  in  a  mesh  of 
fibrous  alveolar  tissue  containing  considerable  fat  in  its  reticu- 
lum. The  ultimate  divisions  of  the  duct  (alveoli)  are  lined  with 
columnar  epithelial  cells,  as  are  the  ducts  and  their  branches,  but 
the  epithelium  of  the  ducts  becomes  flat  (squamous)  near  the  nip- 
ple. The  main  ducts  (lactiferous  duets)  are  sacculated,  and  during 
lactation  the  secretion  of  the  alveoli  collects  in  them,  and  is  drawn 
from  them  through  their  small  orifices  in  the  nipple.  The  flow  of 
milk  is  also  aided  ])y  the  presence  of  a  small  amount  of  unstriped 
muscular  fibre  in  the  wall  of  the  ducts. 

The  mammae  are   abundantly  supplied  with  blood-vessels,  lym- 


68  SECRETION. 

phatics,  and  nerves,  and  during  pregnancy  and  lactation  tlie  ves- 
sels, as  well  as  the  gland,  undergo  considerable  increase  in  size. 

What  is  milk  ? 

The  secretion  of  the  mammary  gland  is  a  bluish-white  fluid.  It 
is  opaque,  and  this  opacity  is  caused  b}"  the  presence  of  minute  fat- 
globules  which  are  held  suspended — an  emulsion.  Besides  the  fat- 
globules  the  microscope  shows  in  milk  from  a  newly-active  gland 
certain  albuminous  bodies  which  are  known  as  colostrum-corpus- 
cles. They  are  probably  cells  from  the  gland  which  are  under- 
going fatty  degeneration.  Milk  is  alkaline  in  reaction,  and  has  a 
sp.  gr.  of  about  1030. 

Describe  the  composition  of  milk. 

The  ingredients  of  milk  are  water,  containing  in  suspension  fats 
and  in  solution  casein,  serum,  albumin,  milk-sugar,  and  salts.  Hu- 
man milk  differs  from  cow's  milk  in  containing  less  proteids  and  fats 
and  more  sugar: 

Human  Milk.  Cow's  Milk. 

Water 890  858 

Proteids    ....    35  68 

Fats 25  38 

Sugar 48  30 

Salts 2  _6 

1000  1000 

What  is  cream? 

The  fat-globules  rise  to  the  top  if  milk  is  allowed  to  stand,  and 
are  called  cream.  By  agitating  or  '■  churning"  the  cream  the  albu- 
minous envelopes  of  the  fat-globules  are  broken,  and  they  coalesce 
to  form  a  fat  mass  known  as  "  butter." 

Why  does  milk  "turn  sour"  ? 

The  addition  of  an  acid  to  milk  causes  the  casein,  which  is  held 
in  solution  by  the  alkaline  sodium  phosphate  present,  to  be  precip- 
itated. The  precipitation  of  the  casein  leaves  behind  the  watery 
and  soluble  ingredients,  but  includes  with  it  the  fat-globules.  The 
precipitate  is  known  as  the  "  curd,"  and  the  watery  residuum  as 
"  whey."  This  process  is  imitated  in  nature  by  the  breaking  up 
of  milk-sugar  (lactose)  to  form  lactic  acid  through  the  action  of  a 
micro-organism,  hactermm  lactis. 


THE  SKIN.  69 

What  is  meant  by  milk-curdling  ferments? 

Certain  feniieiits  will  act  upon  luilk  tu  cause  its  separation  into 
curd  and  whey.  These  arc  called  uiilkcurdling  ferments.  They 
are  found  especially  in  the  secretions  of  the  stomach,  pancreas,  and 
intestine. 

How  is  a  milk-curdling  ferment  utilized  in  the  arts? 

In  cheese  manufacture  the  fourth  stomach  of  the  calf  (rennet) 
is  used  to  curdle  milk. 

What  causes  a  scum  to  form  upon  boiled  milk  ? 
The  serum-albumin  is  solidified  by  heat. 

What  changes  occur  in  milk  at  different  periods  of  lactation  ? 

The  milk  of  mothers  prior  to  and  just  after  parturition  is  known 
as  colostrum,  and  is  deficient  in  casein  and  contains  an  excess  of 
serum-albumin,  as  well  as  colostrum-corpuscles.  Toward  the  end 
of  lactation  there  is  also  said  to  be  the  same  excess  of  serum-albu- 
min and  lack  of  casein. 

How  are  the  fat-globules  of  milk  secreted? 

It  seems  probable  that  two  methods  are  possible  :  (1)  The  epithe- 
lial cells  of  the  gland  seem  capable  of  causing  a  metabolism  of  pro- 
teids  to  form  fat ;  (2)  the  cells  themselves  may  undergo  a  fatty 
metamorphosis. 

What  is  the  value  of  milk  as  a  food  ? 

As  the  food  of  all  young  animals  it  has  to  be  considered  of  the 
greatest  importance ;  besides  this,  as  a  direct  food,  both  in  the 
natural  state  and  in  the  derived  forms  of  butter  and  cheese,  it  is 
one  of  the  most  used  articlesof  adult  diet.  The  causes  which  lead 
to  its  choice  in  the  dietary  are  easily  seen  :  it  contains  all  the  ele- 
ments necessary  to  sustain  life — water,  proteids.  carbohydrates,  and 
salts.  As  an  exclusive  diet  it  will  probably  sustain  life  better  than 
any  other  substance. 

THE   SKIN. 
Describe,  roughly,  the  structure  of  the  skin. 

There  are  two  layers  of  tissue  which  form  the  entire  thickness 
of  the  .skin.  The  superficial  epithelial  layer  is  known  as  the  epiiJer- 
mis  or  cuticle;  the  deeper  stratum,  in  which  lie  the  active  functional 
elements,  is  called  the  cutis  vera,  corium,  or  derma. 


70  SECEETION. 

What  is  the  function  of  the  epidermis  ? 

The  epidermis  is  a  stratification  of  epithelial  cells  of  varying 
thickness.  The  epithelium  is  flat  and  horny  at  the  surface,  in  the 
deeper  portions  are  flattened  and  polyhedral  cells,  and  it  is  closely 
adapted  to  the  surface  of  the  corium  beneath  it.  In  its  deeper 
layer  is  found  the  pigment  which  characterizes  the  complexion  of 
individuals  and  of  races.  Its  function  is  purely  one  of  protection. 
The  growth  to  replace  worn-out  cells  is  very  rapid,  and  in  cases 
of  considerable  use  of  a  part,  with  interrupted  pressure  upon  the 
skin,  the  cuticle  becomes  very  thick  and  horny,  as  is  often  seen 
upon  the  hands  and  feet.  The  hair  and  nails  are  modifications  of 
the  epidermal  epithelium. 

Describe  the  structure  of  the  corium. 

The  true  skin  is  a  tough,  elastic  tissue  composed  of  interlacing 
bundles  of  connective-tissue  cells  containing  spaces  between  the 
fasciculi.  These  spaces  are  known  as  areolse.  There  are  also  num- 
erous unstriped  muscular  fibres.  This  structure  lies  upon  a  more 
or  less  thick  layer  of  fatty  or  loose  cellular  tissue.  In  the  cutis  are 
found  the  active  organs  of  the  skin — the  papillae,  sweat-  and  seba- 
ceous glands,  and  the  hairs  (Fig.  16). 

What  are  the  papillae  and  their  uses  ? 

Upon  the  superficial  surface  of  the  cutis  vera  are  innumerable 
minute  elevations  which  project  into  the  epithelium.  They  are 
very  vascular,  and  contain  the  nerve-endings  which  give  to  the  skin 
its  sensibility,  the  sense  of  touch.  The  papillae  are  especially  abun- 
dant upon  the  parts  in  which  this  sense  is  most  acute — palms,  finger- 
tips, soles. 

Describe  the  sweat-glands. 

Each  gland  lies  in  the  subcutaneous  fat,  and  consists  of  a  con- 
voluted mass  of  tubules  which  terminates  in  a  duct  leading  up 
through  the  derma  and  epidermis,  discharging  the  secretion  of  the 
gland  through  a  minute  opening.  This  secretion  is  known  as  per- 
spiration or  sweat. 

What  is  meant  by  the  term  "  insensible  perspiration  "  ? 

When  the  secretion  of  the  sweat-glands  forms  in  drops  upon  the 
skin,  we  speak  of  this  as  sensible  perspiration  or  sweat.  However, 
at  all  times  the  glands  continue  active  and  the  fluid  evaporates  rap- 


THE   SKIN. 


71 


idly,  so  that  no  moisture  is  noticeable  upon  the  surface  ;  and  we  call 
this  the  insensible  perspiration. 

Fig.  16. 


Sectional  View  of  the  Skin,  magnified. 

What  is  the  sweat  ? 

Tt  is  a  watiTY  fluid,  oolorless.  sli<:htly  turbid,  slightly  salty  to  the 
taste,  of  acid  reaction,  and  possessing  a  peculiar  odor.  It  is  an 
excrement.    Its  composition  is  somewhat  variable,  but  in  general  it 


72  SECEETION. 

may  be  said  to  contain  about  J  per  cent,  of  solids  suspended  and 
dissolved  in  water.  These  solids  are  fats  and  fatty  acids,  sodium 
chloride,  epithelium,  and  a  trace  of  urea.  Besides  these  there  is  a 
considerable  amount  of  carbonic  dioxide  (CO2)  excreted  by  the 
skin. 

What  is  the  amount  of  sweat  excreted  in  twenty-four  hours  ? 

About  one  and  a  half  to  two  pints,  but  this  varies  greatly  with 
the  environment. 

What  factors  affect  the  amount  of  the  sweat  ? 

The  condition  of  the  atmosphere,  the  nature  and  quantity  of  the 
food,  the  amount  of  fluids  consumed,  the  exercise  taken,  and  the 
relative  activity  of  the  other  glands,  especially  of  the  kidneys. 
Certain  mental  conditions,  some  diseases,  and  drugs  also  interfere 
with  sweat-secretion.* 

What  ingredients  produce  the  characteristic  odor  of  perspiration  ? 

The  fatty  acids — formic,  acetic,  butyric,  propionic,  caproie,  and 
caprylic — have  been  found.  The  odor  of  sweat  varies  in  diiferent 
portions  of  the  body. 

Upon  what  nervous '^mechanism  does  the  production  of  perspira- 
tion depend? 

It  is  probable  that  the  sweat-glands  are  under  the  reflex  control 
of  centres  in  the  medulla  and  in  the  spinal  cord,  and  that  these 
centres  regulate  this  function  of  the  skin  through  the  vaso-motor 
system. 

Is  sweat-excr.etion  necessary  to  life  ? 

Yes,  because  of  the  disturbance  of  heat-regulation  by  absence  of 
evaporation,  or,  perhaps,  by  absorption  or  retention  of  poisonous 
matter.  The  symptoms  are  those  of  an  acute  poisoning — pyrexia 
and  exhaustion. 

What  is  the  character  of  the  sebaceous  glands  ? 

The  sebaceous  glands  occur  everywhere  over  the  entire  skin  sur- 

*  Under  conditions  which  exaggerate  the  flow  of  the  perspiration,  as  hard 
work  in  hot  air,  with  free  consumption  of  fluids,  the  amount  of  the  perspi- 
ration is  said  to  exceed  twenty  pints  in  a  day. 


THE   KIDNEYS   AND  THE   URINE.  73 

face  with  the  exception  of  the  palms  and  soles,  and  most  abun- 
dantly in  the  hairy  parts.  They  are  intimately  connected  with 
the  hair-follicles,  and  their  ducts,  as  a  rule,  open  into  the  folli- 
cles, though  sometimes  they  discharge  separately.  The  glands  are 
aggregate  glands  ;  that  is,  are  formed  by  the  subdivision  of  the  duct 
to  make  up  the  lobules  of  the  gland.  There  is  a  delicate  plexus 
of  capillary  vessels  about  the  sacculi. 

What  do  they  secrete  ? 

The  secretion  of  the  sebaceous  glands  is  a  soft,  oily,  white  mate- 
rial, and  has,  besides  other  fats,  stearin  for  basis.  Its  use  seems  to 
be  to  lubricate  the  skin,  keeping  it  soft  and  flexible,  and  at  the  same 
time,  by  its  oily  nature,  to  prevent  maceration  of  the  skin  by  con- 
tinued exposure  to  moisture,  and  to  check  the  undue  absorption 
from  the  surface.  Sebaceous  matter  is  not  excrementitious,  but 
is  a  secretion. 

Has  the  skin  power  to  absorb  ? 

It  has.  This  function  of  the  skin  is  utilized  in  the  application 
of  medicines,  of  food,  and  of  drink  in  appropriate  cases. 

What  further  function  has  the  skin  ? 
That  of  regulation  of  body -temperature. 

THE  KIDNEYS   AND   THE  URINE. 
Describe  the  gross  appearance  of  the  kidneys. 

The  kidneys  are  glandular  organs  having  somewhat  the  form  of 
a  bean.  In  size  they  are  somewhat  more  than  4  inches  in  length, 
somewhat  more  than  2  inches  wide,  and  about  1  inch  thick.  The 
weight  of  each  organ  is  about  4  to  6  ounces.  A  thin  but  rather 
tough  capsule  invests  the  kidney  (Fig.  17).  This  may  be  pulled 
off  readily,  leaving  the  surface  of  the  organ  smooth  and  even  and 
of  a  deep-red  color.  If  a  vertical  section  of  the  organ  be  made, 
the  central  cavity  (sinus)  will  be  noticed,  and  about  it  the  kidney 
tissue.  Within  the  sinus  are  the  apices  of  pyramidal  projections. 
about  ten  in  number,  and  if  the  cut  surface  be  examined  closely  it 
may  be  noted  that  the  outer  (cortical)  portion  differs  in  appearance 
from  the  more  central  (medullary)  portion.  The  blood-supply  is 
from  the  renal  artery,  and  the  nerve-supply  is  from  the  sympathetic 
system  through  the  solar  plexus. 


74 


SECEETION. 


What  is  the  function  of  the  kidney  ? 

The  secretion  of  the  urine.     The  kidney  is  a  compound  tubular 
gland.      The   medullary  portion  of  the  organ  is  almost  entirely 

Fig.  17. 


Vertical  Section  of  Kidney. 


made  up  of  tubules,  which  take  origin  in  the  cortex  and  empty 
upon  the  apices  of  the  pyramids  of  Malpighi  of  the  medullary 
portion. 

What  are  the  Malpighian  bodies? 

In  the  cortical  portion  of  the  kidneys  are  found  minute  tufts  of 


THE   KIDNEYS   AND   THE   URINE. 


75 


capillaries  which  are  .surrouiuled  by  a  capsule  lined  by  epithelial 

cells  (Fig.  IS),  and  here  it  it  is  that  the  urin- 

iterous   tubules    arise,  the  tuft  of    capillary  Fio.  18. 

vessels  being,  as  it  were,  built  into  the  end 

of  the  tubule. 

What  are  the  uriniferous  tubules? 

BoyiMning  in  the  curti'X  of  the  kidney  at 
one  of  the  bodies  of  Malpighi,  the  minute 
secreting  ducts  pursue  a  tortuous  course  to 
the  larger  collecting  tubules,  which  empty  at 
the  apices  of  the  pyramids  of  Malpighi  into 
the  calyces  of  the  kidney.  Without  entering 
minutely  upon  the  course  of  the  tubules,  it  is 
important  to  remember  that  they  form  a  loop 
(of  Henle)  which  dips  into  the  pyramid,  and 
that  they  pursue  a  somewhat  tortuous  course 
both  before  entering  into  the  loop  of  Henle 
and  upon  returning  to  the  cortical  portion  of 
the  kidney,  where  they  empty  into  the  straight  collecting  tubules. 
The  straight  course  of  the  arms  of  Henle's  loop  and  of  the  collect- 
ino-  tubules  gives  to  the  pyramids  a  finely  striated  apppearauce. 
(See  Fig.  19.) 


Malpighi.in  Body. 


Describe  the  blood-circulation  in  the  kidney. 

On  entering  the  kidney  the  renal  artery  breaks  up  into  several 
])ranches,  which  pass  into  the  tissue  proper  of  the  organ.  Branches 
from  these  arteries  (arteria  propria  renales)  have  two  determina- 
tions— (1)  into  the  cortex,  and  (2)  into  the  pyramids. 

(1)  Those  branches  (interlobular)  which  pass  into  the  cortex 
divide  to  become  the  ajferent  vessels  to  the  jMalpighian  bodies,  and, 
after  there  passing  through  the  capillary  tuft,  the  blood  is  re-col- 
lected and  goes  out  by  an  efferent  vessel.  This  efferent  vessel  in 
its  turn  is  broken  into  a  minute  capillary  plexus  which  surrounds 
the  uriniferous  tubules  in  the  cortex  of  the  kidney,  and  these 
capillaries  unite  to  form  the  venous  return  circulation.  Thus,  //(**• 
si/sfem  hatf,  it  in  to  he  noted,  tiro  capiflari/  divisions,  in  the  Maljjighian 
tii/t.  and  again  about  the  tuhides  of  the  cortex. 

(2)  Numerous  minute  branches  (arterise  rectae)  are  given  off, 
which  pass  into  the  pyramids,  surround  the  portion  of  the  urin- 
iferous  tubule  (Henle's  loop)  which  passes   into  the   medullary 


76 


SECEETION. 
Fig.  19. 


Arterise  rectse 


Vense  rectae. 


Diagram  of  the  Tubules  and  Vascular  Supplj'  of  the  Kidney.  On  the  left  is  a  tubule 
alone ;  in  the  middle  is  a  tubule  along  with  the  blood-vessels  ;  on  the  right  are  blood- 
vessels only. 

region  of  the  kidney,  and  return  (venae  rectge)  to  join  the  branches 
from  the  cortex  and  form  the  ven^e  propriae  of  the  kidney. 

How  do  the  kidneys  secrete  urine  ? 

(1)  By  filtration,  and  (2)  by  real  functional  action  of  the  epi- 
thelium. 

(1)  In  the  circulation  of  the  blood  through  the  Malpighian  tuft 
there  seems  to  be  no  active  separation  of  the  urinary  ingredients 


THE  KIDNEYS   AND   THE   URINE,  77 

by  cell-power,  but  the  water  and  saline  elements  are  given  off  here 
by  the  bli)od  by  a  pnjcess  uf  simple  filtration.  The  amount  of 
fluid  which  passes  here  is  governed  by  the  blood-pressure  in  the 
arteries  of  the  kidney  and  by  tlie  fluidity  of"  the  blood. 

(2)  The  epitheliiini  of  the  uriniferous  tubules  has  secreting 
fmictiun,  and  is  able  to  firfxtra/e  from  the  blood  foreign  substances 
{<'■</■  indigo-carmine)  and  eject  them  into  the  tubules,  and  to  man- 
ii/'(icfi(rc  from  material  taken  from  the  blood  new  substances  not 
found  there  (('.  ^.  urea  and  pigments). 

What  is  the  course  of  the  urine  after  leaving  the  kidney  ? 

The  urine  collected  in  the  tubules  of  the  kidney  passes  into 
the  pelvis,  and  is  carried  to  the  urinary  bladder  in  irregular  quan- 
tities by  the  ureter.  The  ureters  simply  act  as  ducts,  and  do 
not  store  up  urine,  nor  do  they  usually  actively  eject  it  into  the 
bladder.  As  a  few  drops  of  urine  collect  in  the  pelvis  of  the  kid- 
ney, they  run  into  the  bladder,  the  action  of  the  two  kidneys  not 
being  in  alternation  nor  absolutely  regular  in  point  of  time.  Re- 
gurgitation from  the  bladder  is  prevented  by  the  oblique  course 
of  the  ureter  through  the  muscular  wall  of  the  bladder. 

Describe  the  act  of  micturition. 

When  the  bladder  is  filled  the  act  of  emptying  it  is  called  mictu- 
rition. It  is  a  voluntary  act,  aided  by  the  involuntary  reflex  con- 
traction of  the  muscular  coat  of  the  organ  itself.  The  voluntary 
muscles  involved  are  those  of  respiration — the  diaphragm  and  the 
abdominal  muscles.  So  far  as  micturition  is  involuntary,  it  is  a 
reflex  depending  upon  a  centre  in  the  lumbar  spinal  cord. 

What  are  the  physical  characteristics  of  normal  urine  ? 

It  is  a  clear,  amber-colored  fluid  of  slightly  acid  reaction.  It 
may  develop  a  flocculent  precipitate  of  a  light  cloud  of  mucus  upon 
standing.     It  has  a  characteristic  odor  and  a  salty-bitter  taste. 

What  is  the  normal  specific  gravity  of  the  urine  ? 

About  1020,  but  under  conditions  of  health  it  may  vary  from 
1010  to   lOP.O.  or  even   beyond  these  limits. 

What  conditions  afifect  the  acidity  of  the  urine  ? 

The  acidity  of  the  urine  is  due  to  the  presence  of  acid  sodium 
])hosphate.  There  is  no  free  acid  present,  as  is  shown  by  the  fact 
that  no  precipitate  is  formed  upon  the  addition  of  sodium  hyposul- 
l)hite.     The  degree  of  acidity  varies,  being  less  during  active  diges- 


78 


SECRETION. 


tion  and  less  after  vegetable  food.  Herbivora  have  alkaline  urine, 
while  carnivora  have  strongly  acid  urine ;  but  the  herbivorous  ani- 
mal during  fasting  has  acid  urine,  because  it  is  then  living  from  its 
own  tissues  and  is  for  the  time  a  carnivore.  After  excretion,  how- 
ever, the  urine  soon  becomes  more  acid  (probably  because  of  the 
presence  of  some  fermentation),  and  at  this  time  uric  acid  and 
urates  may  precipitate.  Upon  further  exposure  it  is  attacked  by 
micro-organisms,  and  the  urea  is  changed  to  ammonium  carbonate, 
the  reaction  becoming  alkaline,  and  there  is  a  precipitation  of  triple 
phosphates  and  alkaline  urates.  In  the  body  these  conditions  do 
not  occur  in  conditions  of  health. 

What  is  the  chemical  composition  of  urine  ? 

The  urine  is  an  excrementitious  fluid,  and  may  be  considered  as 
a  watery  solution  of  the  excrementitious  products  of  the  retrograde 
metamorphosis  of  nitrogenous  bodies,  resulting  from  the  processes 
of  life  and  action.  Chemically,  it  is  a  solution  of  urea  and  urates 
with  a  small  percentage  of  organic  salts. 

Tahle  of  the  Cliemical  Composition  of  the  Urine. 

Water 967 

Solids,  crystallizable  nitrogenous  bodies  : 

Urea 14 

Uric  acid,  free  (trace), 
Uric  acid  in  form  of  alkaline  urates, 

Hippuric  acid  and  hippurates,  V  .       11 

Pigments,  extractives,  and  mucus, 
All  in  small  and  constant  amounts. 
Salts : 

Inorganic — 

Chlorides  of  sodium  and  potassium, 

Sulphates  and  phosphates  of  sodium  and  potas- 
sium. 

Phosphates  of  magnesium  and  calcium, 

Silicates  (trace), 
Organic — 

Lactates,    acetates,  and  formates,  which   only 
appear  occasionally, 
Sugar  (occasionally),  a  trace, 
Gases,  nitrogen,  and  carbonic  acid. 

Tooo 


THE   KIDNEYS   AND   THE    URINE.  79 

What  is  the  daily  quantity  of  urine  secreted  ? 

One  to  two  (jiiarts.  The  (juaiitity  varies  greatly  in  health  with 
the  Amount  of  fluid  taken,  of  food  consumed,  of  the  activity  of  the 
skin  evaporation,  and  somewhat  with  the  character  of  the  food.  In 
a  more  general  way  it  may  be  said  to  depend  upon  the  condition  of 
the  blood,  an  excess  of  fluids  demanding  increase  of  functional  ac- 
tivity on  the  part  of  the  kidneys.  In  conditions  of  disease  or  under 
the  stimulus  of  drugs  the  limits  mentioned  are  by  no  means  final, 
for  in  certain  pathological  conditions  the  secretion  may  be  almost 
wholly  suspended  or  very  greatly  increased. 

What  conditions  increase  the  urinary  secretion? 

The  conditions  which  favor  filtration  of  water  by  the  glomeruli 
of  Malpighi ;  that  is,  the  presentation  of  a  larger  amount  of  blood 
to  the  action  of  these  bodies.     This  is  accomplished — 

(1)  By  increasing  the  force  of  the  heart. 

(2)  Through  the  nervous  system  by  its  action  upon  the  vascular, 
so  as  to  produce  local  congestion.  The  effect  of  the  nervous  sys- 
tem in  increasing  the  urine  by  reflex  vaso-motor  impulses  is  felt 
most  in  the  glomeruli,  and  the  urine  is  therefore  very  watery. 

(o)  Conditions  which  cause  anaemia  of  other  parts  may  produce 
a  greater  determination  of  blood  to  the  kidneys,  and  so  increase 
the  urinary  flow.  So  marked  is  this  that  the  skin  and  kidneys 
may  almost  be  said  to  be  complementai'y  in  their  action  in  elimi- 
nating water  from  the  system  ;  and  in  this  regard  their  relative 
activity  may  be  said  to  be  inversely  proportional  to  one  another. 

Kirke  has  the  following  table  (modified  from  Foster),  which  is 
useful  for  reference : 

Table  of  the  Relation  of  the  Secretion  of  Urine  to  Arterial  Pressure 

(Kirke). 

A.  Secretion  of  urine  may  be  increased — 

a.  Biy  increasing  the  general  hlood-pressure — by 

1.  Increase  of  the  force  or  frequency  of  heart-beat. 

2.  Constriction  of  the  small  arteries  of  areas  other  than  that 

of  the  kidney. 
h.   By  increasing  the  local  blood-pressure  by  relaxation  of  the  renal 
artery ^  without  compensating  relaxation  elsewhere — by 

1.  Division  of  the  renal  nerves  (causing  polyuria). 

2.  Division  of  the  renal  nerves  and  stimulation  of  the  cord, 

below  the  medulla  (causing  greater  polyuria). 


80  SECEETION. 

3.  Division  of  the  splanchnic  nerves ;  but  the  polyuria  pro- 

duced is  less  than  in  1  or  2,  as  these  nerves  are  distrib- 
uted to  a  wider  area,  and  the  dilatation  of  the  renal 
artery  is  accompanied  by  dilatation  of  other  vessels,  and 
therefore  with  a  somewhat  diminished  general  blood- 
supply. 

4.  Puncture   of  the   floor   of  fourth  ventricle  or  mechanical 

irritation  of  the  superior  cervical  ganglion  of  the  sympa- 
thetic, possibly  from  the  production  of  dilatation  of  the 
renal  arteries. 
B.  Secretion  of  urine  may  be  diminished — 

a.  By  diminishing  the  general  blood-p^'essiio'e — by 

1.  Diminution  of  the  force  or  frequency  of  the  heart-beats. 

2.  Dilatation  of  capillary  areas  other  than  that  of  the  kidney. 

3.  Division  of  spinal  cord  below  the  medulla,  which  causes 

dilatation  of  general  abdominal  area,  and  urine  generally 
ceases  being  secreted. 

b.  By  increasing  the  hhod-pressure — by  stimulation  of  the  spinal 

cord  below  the  medulla,  the  constriction  of  the  renal 
artery  which  follows  not  being  compensated  for  by  the 
increase  of  general  blood-pressure. 

c.  By  constriction  of  the  renal  artery — by  stimulating  the  renal  or 

splanchnic  nerves  or  the  spinal  cord. 

What  two  methods  of  elimination,  then,   do  we  find  in  the 
kidneys  ? 

(1)  The  process  of  filtration,  depending  upon  blood-pressure  and 
acting  almost  solely  upon  the  aqueous  elements. 

(2)  Secretion  proper,  by  which  cell-activity  performs  the  func- 
tion of  excreting  the  solid  matters  of  the  urine. 

What  is  the  source  of  the  urea? 

It  is  not  fully  known  whether  the  urea  is  taken  from  the  blood 
as  such  by  the  kidneys,  or  if  it  is  made  up  by  the  cells  of  the  kid- 
neys from  elements  taken  from  the  blood.  It  is  probable  that  the 
former  is  for  the  most  part  the  source  of  urea,  and  a  less  amount 
is  really  composed  in  the  cells  of  the  kidney-tubules.  At  any  rate, 
the  source  of  the  urea  is  the  nitrogenous  matters  of  the  body  :  1, 
those  taken  in  as  food,  urea  being  greatly  increased  by  a  nitrog- 
enous meal ;  2,  by  the  metabolism  of  the  tissues.  The  measure 
of  the  amount  of  work  done  is,  however,  not  found  in  the  quantity 


THE   VASCULAR   GLANDS.  81 

of  urea  excreted.  The  secretion  of  urea  continues  if  nitrogenous 
food  he  absent  from  the  diet ;  and  the  elimination  is  increased  by 
increased  cell-activity,  and.  consequently,  of  cell-degeneration,  as 
by  muscular  work. 

What  is  the  amount  of  urea  excreted? 

The  amount  varies,  but  it  may  be  considered  to  be  about  one- 
half  the  solid  constituents  of  the  urine.  Koughly  speaking,  the 
urinary  solids  may  be  regarded  as  4  per  cent,  of  the  total,  and 
the  urea  (including  the  uric  acid  and  urates)  about  1.5  to  5  per 
cent.  This  proportion  is  very  variable,  and  there  may  be  urea  in 
healthy  urine  to  exceed  2h  per  cent.,  or  in  a  much  less  ratio  than 
5  per  cent. 

Metliod  of  Estimating  Solids. — A  useful  rule  for  approximately 
estimating  the  total  solids  in  any  given  specimen  of  healthy  urine 
is  to  multiply  the  last  two  figures  representing  the  specific  gravity 
by  2.33.  Thus,  in  urine  of  sp.  gr.  1025,  25  X  2.33  =  58.25  gr.  of 
solids  in  1000  gr.  of  urine.  In  using  this  method  it  must  be  re- 
membered that  the  limits  of  error  are  much  wider  in  diseased  than 
in  healthy  urine. 

What  abnormal  matters  are  sometimes  found  in  urine  ? 

In  disease  or  after  the  introduction  of  certain  foods  we  ma}'  find 
certain  abnormal  elements  in  urine — serum-albumin,  globulin,  fer- 
ments, peptone,  blood,  sugar,  bile  acids  and  pigments,  casts,  fats, 
micro-organisms,  etc. 

THE   VASCULAR  GLANDS. 

What  is  meant  by  the  term  "vascular  glands"? 

Certain  glandular  organs  which  are  made  up  largely  of  lym- 
phatic tissues,  but  which  do  not  seem  to  be  connected,  at  least 
directly,  with  secretion  or  excretion.  Among  those  glands  may  be 
mentioned,  as  the  more  noticeable,  the  spleen,  the  thymus  gland, 
the  thyroid  gland,  the  tonsils,  the  suprarenal  capsules,  the  pineal 
and  the  pituitary  glands,  and  Peyer's  glands. 

What,  in  a  general  way,  is  the  function  of  the  vascular  glands  ? 

This  cannot  be  fully  answered,  as  the  subject  is  not  understood 
at  all  completely  ;  but  it  may  be  said  that  their  work  has  probably 
to  do  with  the  elaboration  of  the  blood,  and,  further,  that  each  of 

6— Phy. 


82  MUSCLE. 

the  glands  has  an  unknown  special  office  beyond  the  function  of 
maintaining  a  constant  supply  of  red  and  white  blood-corpuscles, 
and  of  caring  for  them  when  past  usefulness.  Such  an  opinion  is 
based  upon  the  disturbance  of  the  special  glands  in  certain  diseases, 
and  upon  the  great  activity  of  these  glands  during  foetal  and  infant 
life,  when  the  elaboration  of  the  blood  is  necessarily  very  rapid  to 
maintain  rapid  development.  In  function,  as  well  as  in  structure, 
these  glands  are  similar  to  lymph-glands. 

Has  the  spleen  a  special  function? 

The  spleen  becomes  considerably  increased  in  size  during  diges- 
tion of  food,  and  the  tissue  of  the  organ  becomes  filled  with 
albuminous  particles  which  gradually  disappear,  and  hence  it  is 
inferred  that  there  are  special  functions  which  have  to  do  with  the 
elaboration  of  the  nitrogenous  foods.  Besides  this,  the  spleen  may 
be  regarded  as  a  prominent  source  of  origin  of  both  red  and  color- 
less blood-corpuscles,  and  as  the  organ  in  which  many  of  the  red 
corpuscles  undergo  degeneration  when  their  usefulness  is  impaired. 
Furthermore,  it  is  a  very  vascular  organ,  and  is  capable  of  very 
great  iistension,  and  becomes,  in  a  passive  way,  a  sort  of  safety- 
valve  'in  relieving  the  portal  system,  more  especially  of  the 
stomach. 

Can  any  special  function  be  attributed  to  any  other  of  the  vascu- 
lar glands? 

No. 

MUSCLE. 

What  kinds  of  muscular  tissue  are  found  ? 

1,  plain  or  unstriated  muscle-fibres  ;  2,  striated  muscle-fibres. 

Describe  the  unstriped  or  plain  muscles. 

They  are  found  in  the  tissues  in  which  the  will  has  no  control, 
and  are  known  as  involuntary  muscles.  These  muscles  are  made  up 
of  bundles  of  elongated,  spindle-shaped  cells.  Each  cell  has  an 
oblong  nucleus  and  is  flattened  (Fig.  20).  In  length  they  are  about 
-g-^g-  to  g-^Q-  inch,  and  about  -^-^-^-^  inch  in  width.  The  cells  are 
bound  into  bundles  by  an  albuminous  cement,  and  these  again 
into  larger  bundles  by  areolar  tissue. 

What  is  the  appearance  of  the  striated  muscle  ? 

This  form  of  muscle-tissue  makes  up  the  most  of  the  bodily 
tissue,  for  it  is  found  in  all  of  the  voluntary  muscles.     All  such 


MUSCLE. 


83 


muscles  arc  made  up  of  fasciculi  of  fibres  of  this  striat 
tissue,  each  bein^   enclosed  in  a  sheath  (surcolemma) 
The   arrangement  of  the   elements   of  each 
fibre  is  such  that  its  microscopic  appearance  Fir;, 

is  as  though  there  were  alternate  light  and  A. . 

dark  bands  about  it.  the  dark  being  the 
wider.  These  are  the  elements  of  the  muscle- 
tissue,  the  dark  bands  representing  disks  of 
contractile  tissue,  while  the  brighter  bands 
represent  a  disk  of  interstitial  substance. 

What  are  sarcous  elements? 

The  fibres  may  be  split  up  longitudinally 
into  minuter  fibrils  which  have  the  micro- 
scopic appearance  of  alternate  light  and 
dark  particles ;  these  particles  are  the  sar- 
cous elements  (Fig.  21,  B,  d).  and  it  is  b}' 
the  fusion  of  these  fibrils  that  the  fibres  are 
made  up. 

How  large  are  striped  muscle-fibres? 

They  are  about  an  inch  in  length  and 
■j^  inch  in  diameter.  They  join  the  con- 
nective-tissue cells  of  a  tendon  or  aponeu- 
rosis or  another  muscle-fibre  by  adhesion  of 
the  sareolemma  at  the  ends,  and  thus  unite 
the  muscle-bundles  in  a  firm  mass ;  and  this 
union  is  further  strengthened  by  the  cohe- 
sion of  the  fibres. 


ed  m 


uscle- 
.  21). 


Non-striated  Elementary 
Fil)res,  from  the  human 
colon :  a,  treated  with 
acetic  acid,  showing  the 
corpuscles :  b,  fragment 
of  a  detached  fibre  not 
touched  with  acid. 


What  is  peculiar  in  the  heart-muscle? 

It  is  an  exception  to  the  rule  that  involuntary  muscles  are  un- 
striped.  The  striation  of  the  heart-muscle  fibres  is  not  so  marked 
as  in  ordinary  muscle,  and  the  form  of  the  fibres  is  different,  for 
they  are  branched  and  more  slender.  Each  fibre  is  nucleated,  a 
large  oval  nucleus  occurring  at  the  centre.  The  appearance  of 
the  heart-fibres  indicates  that  they  occupy  an  intermediate  position 
between  typical  plain  and  striped  fibres. 

What  is  myosin? 

Myosin  is  an  albuminoid  substance  belonging  to  the  class  of 


84 


A,  Portion  of  a  Medium-sized  Human  Muscular  Fibre  (magnified  nearly  800  diameters). 

B,  Separated  Bundles  of  Fibrils,  equally  magnified :  a,  a,  larger,  and  6,  6,  smaller  collec- 

tions; c,  still  smaller;  d,  d,  the  smallest  which  could  be  detached. 


globulins,  which  may  be  derived  from  muscle.  This  substance 
bears  the  same  relation  to  living  muscle  that  plasma  does  to  living 
blood.  By  pressing  muscle  kept  at  a  temperature  below  the  freez- 
ing-point it  is  possible  to  obtain  a  viscid,  opalescent  fluid  of  alkaline 
reaction,  which  soon  presents  the  phenomenon  of  clotting,  and  one 
has  resulting  a  muscle-senim  and  mvscle-clot.  This  muscle-clot  is 
myosin.  During  the  process  the  fluid  becomes  acid  in  reaction. 
The  clotting  of  muscle-plasma  is  caused  (probably)  by  ferment 
action,  and  the  ferment  (myosin-ferment)  is  derived  from  a  com- 
posite antecedent,  similar  to  fibrinogen,  called  myosinogen. 

What  gives  muscle  its  red  color? 

Haemoglobin  of  the  blood  in  some  degree ;  but  there  is  also  a 
distinct  pigment  known  as  myo]i8e,inaturin. 


MUSCLE.  85 

What  is  tlie  chemical  composition  of  muscle  ? 

Water  is  a  cliict'  intrredieut,  and  myosin  the  characteristic  one. 
Salts  arc  found,  chiefly  of  potassium.  A'arious  proteids,  such  as 
gehxtin,  ehistic  material,  and  al))uniins,  are  found,  together  with 
fats  and  extractives.  The  extractives  are  mostly  complex  organic 
compounds  :  among  them  may  be  mentioned  kreatin,  lactic  acid, 
and  sugar.  Urea  is  not  found,  except  in  minute  quantities,  though 
it  is  regarded  as  origiiuiting  from  the  waste  products  of  muscular 
action.  The  following  table  formulates  the  proportion  of  these  con- 
stituents : 

Water 745 

Solids : 

Myosin  and  insoluble  proteids 155 

Soluble  proteids 20 

Gelatin 21 

Fats 23 

Organic  and  inorganic  salts 36 

1000 
What  is  the  reaction  of  live  muscle  ? 

Alkaline,  due  to  the  presence  of  potassium  phosphate. 

What  is  the  function  of  the  muscles  ? 

They  contract  and  cause  motion  in  the  parts  to  which  they  are 
attached.  During  life  the  muscles  are  always  tense,  and  this  con- 
dition favors  a  more  powerful  action  when  the  muscles  contract  in 
response  to  stimuli. 

How  do  the  muscles  affect  the  blood  passing  through  them  ? 

They  abstract  much  of  the  oxygen  and  give  oft'  large  amounts 
of  carbonic  acid,  so  that  blood  after  circulating  through  the  mus- 
cles, even  when  they  are  at  rest,  becomes  very  dark.  It  is  prol)able 
that  an  abundance  of  oxygen  is  especially  essential  to  the  healthy 
condition  of  the  muscles,  and  it  is  found  that  in  an  atmosphere  of 
oxygen  muscles  retain  their  power  of  contraction  longer  than  in 
one  of  hydrogen  or  carbonic  acid. 

What  peculiar  electrical  condition  is  noticed  in  living  muscle  ? 

When  a  living  muscle  is  tested  by  means  of  the  galvanometer 
after  removal  from  the  body,  it  is  found  to  develop  certain  electri- 
cal currents  known  as  muscle-currents  or  currents  of  rest.     They  are 


86  MUSCLE. 

strongest  from  the  centre  of  the  muscle  toward  the  cut  end,  though 
certain  minor  currents  are  developed  with  the  electrodes  in  closer 
proximity.  The  cut  ends  of  a  muscle  are  always  electro-negative 
to  its  equator.  This  phenomenon  cannot  be  observed  in  uninjured 
muscle  when  in  the  body,  but  any  injury  will  render  the  injured 
portion  electro-negative  to  the  rest  of  the  muscle.  This  condition 
ceases  with  the  power  of  contraction,  and  cannot  be  demonstrated 
in  dead  muscle. 

What  is  the  effect  of  contraction  upon  this  "current  of  rest"? 

When  the  muscle  is  made  to  contract,  the  galvanometer  needle, 
which  has  indicated  the  passage  of  an  electrical  current  during  rest, 
flies  quickly  back  toward  the  zero  indicating  the  cessation  of  the 
current  of  rest.  This  action  is  known  as  the  negative  variation  of 
the  galvanometer,  and  as  soon  as  the  contraction  of  the  muscle  has 
ceased  the  instrument  again  indicates  the  presence  of  the  current 
of  rest. 

What  is  the  cause  of  these  electrical  currents  ? 

This  is  not  yet  fully  determined,  but  they  are  probably  due  to 
chemical  changes  resulting  from  the  physiological  degeneration.  It 
has  been  held  that  such  currents  occur  naturally  in  muscle  as  the 
result  of  certain  of  the  cells  exciting  electro-motive  forces,  but  the 
former  theory  seems  the  more  plausible. 

What  stimulus  causes  a  muscle  to  contract? 

The  stimulus  is  supplied  by  the  motor  nerve  which  is  distributed 
to  the  muscle. 

How  do  the  motor  impulses  reach  the  fibres? 

The  nerve  divides  and  subdivides  in  the  muscle  until  only  a 
single  axis-cylinder  is  supplied  to  a  small  group  of  muscle-fibres. 
This  axis-cylinder  then  forms  a  delicate  plexus  about  the  muscle- 
fibres,  and  in  the  case  of  plain  muscle-fibres  ends  in  the  nucleus  of 
the  fibre.  In  the  striped  fibres  there  is  a  special  termination  in  a 
small  granular  mass  called  the  motorial  end-plate. 

Is  the  property  of  contraction  inherent  in  the  muscle  itself,  or 
does  it  depend  upon  the  nerve? 
It  is  a  property  of  muscle. 

What  artificial  stimuli  may  be  used  to  cause  muscular  contrac- 
tion? 
Certain  stimuli  may  be  applied  to  a  muscle  or  to  the  nerve  sup- 


MUSCLE.  87 

plying  it  which  excite  it  to  action.  It  is  mure  usual  to  stimulate 
the  nerve,  as  this  is  more  convenient  and  more  effectual.  There 
are  four  kinds  of  excitants  that  may  he  used  :  1,  mechanical,  as  hy 
a  hlow  or  prick  or  pinch  ;  2,  heat,  as  hy  a  hot  needle  ;  8,  chemical, 
as  dilute  acids,  etc. ;  4,  electrical,  as  by  the  galvanic*or  faradic  cur- 
rent. This  is  the  most  usual  as  well  as  most  convenient  kind  of 
stimulus  for  experiment. 

How  are  the  phenomena  of  a  contraction  observed  ? 

They  are  connnoiily  observed  in  a  tracing  upon  an  instrument 
called  the  myograph,  and  usually  a  large  muscle  of  a  frog  and  its 
nerve  are  taken  for  the  demonstration.  The  time  of  the  observa- 
tion is  recorded  by  the  vibrations  of  a  tuning-fork.  Such  a  pi'epa- 
ratiou  is  known  as  "  a  nerve-muscle  preparation,"  and  the  tracing 
obtained  is  called  a  ''  muscle-curve." 

At  what  period  of  an  electrical  current  do  the  muscles  contract  ? 

Only  at  the  making  and  breaking.  If  a  nerve-muscle  prepara- 
tion be  arranged  for  experiment  and  stimulus  be  applied  by  means 
of  a  galvanic  cell,  it  will  be  found  that  the  muscle  will  contract 
only  at  the  instant  the  circuit  is  completed  and  at  the  instant  it  is 
broken.  During  the  time  the  current  is  pas.si}iff  no  contractions  of 
the  muscle  occur,  unless  the  character  of  the  current  changes  or 
the  strength  of  the  current  is  considerable.  The  mere  passage  of 
an  electrical  current  does  not  cause  a  muscle  to  contract,  but  the 
entrance  or  exit  of  the  current  is  the  stimulus.  It  does  not  matter 
if  the  positive  pole  be  applied  to  the  nerve  nearer  the  muscle,  or  if 
the  negative  pole  is  the  nearer :  the  contraction  is  the  same  with 
an  ascending  as  with  a  JcscenJuiff  current. 

Describe  the   phenomena  observed  in  a  single  contraction  fol- 
lowing a  stimulus. 

There  is  a  brief  period  during  which  no  action  occurs,  the  latent 
period,  during  which  the  stimulus  applied  to  the  nerve  is  being 
transmitted  to  the  muscle.  Then  follows  a  sharp,  sudden  contrac- 
tion of  the  muscle  (stage  of  contraction),  which  is  intensified 
steadily  to  a  maximum,  and  then  the  muscle  more  slowly  relaxes 
(stage  of  elongation),  and  the  muscle  returns  to  its  former  condi- 
tion of  rest.  There  are  sometimes  less  violent  contractions  which 
follow,  and  are  due  to  the  elasticity  of  the  musi-le.  The  whole 
time  consumed  is  about  one-tenth  of  one  second,  and  of  this  time 


»»  MUSCLE. 

the  latent  period  and  the  stage  of  contraction  consume  only  about 
one-tenth  each.  • 

What  is  tetanus  ? 

When  the  stimuli  follow  one  another  in  rapid  succession  the  con- 
tractions are  practically  constant,  and  the  stage  of  elongation  does 
not  follow.  This  condition  is  known  as  tetanus.  The  stimuli  may 
be  slow  enough  to  allow  perceptible  quivering  of  the  muscle  (and 
a  wavy  tracing  of  the  myogram),  or  may  be  very  rapid,  so  as  to 
keep  the  contraction  constant. 

What  effect  has  fatigue  upon  the  muscle  ? 

Its  latent  period  is  longer  and  the  strength  of  the  contractions 
diminish. 

Is  the  temperature  of  muscle  elevated  by  action  ? 

Yes.  It  has  been  estimated  that  the  temperature  of  the  biceps 
muscle  may  be  elevated  one  to  two  degrees  of  the  Fahrenheit  scale 
by  exercise.  It  is  not  known  whether  this  is  due  to  chemical 
action  or  to  friction  between  the  fibres. 

How  does  the  shape  of  the  muscle  change  in  contraction  ? 

The  muscle  becomes  shorter,  thicker,  and  harder,  and  seems  to 
bulge  at  the  centre.  This  is  not  an  actual  increase  in  bulk,  for 
what  is  gained  in  thickness  is  made  up  in  the  loss  by  shortening. 
Each  fibre  of  the  muscle  contracts  and  becomes  short  and  thick, 
as  does  the  whole  muscle.  This  shortening  is  due  to  an  approxi- 
mation of  the  elements  probably,  and  not  to  a  change  in  the 
arrangement  of  the  elements. 

What  chemical  changes  occur  in  muscle  with  action? 

The  muscle  (in  rest  alkaline)  becomes  acid  from  the  develop- 
ment of  lactic  acid,  and  there  is  found  a  kind  of  glucose  known  as 
inosite,  or  "  muscle-sugar."  Besides  this,  the  active  metabolism 
increases  the  production  of  carbonic  acid  and  of  extractives. 

What  is  rigor  mortis? 

When  a  muscle  is  dead  it  will  no  longer  respond  to  stimuli,  but 
remains  in  a  contracted  state,  fixing  the  limbs  and  body  in  rigid 
condition.  This  post-mortem  rigidity  constitutes  rigor  mortis. 
The  muscles  of  the  neck  and  jaw  are  usually  first  afiected,  and 


NUTRITION.  89 

then  of  the  arms,  gradually  passing  downward  until  the  whole 
body  is  stiff.  This  begins  usually  soon  after  death,  but  may  be 
delayed  for  several  hours,  and  lasts  until  putrefactive  changes  have 
set  in,  when  the  body  relaxes.  All  muscles  are  affected,  plain  as 
well  as  striped. 

What  is  tlie  cause  of  rigor  mortis  ? 
Coagulation  of  the  muscle-plasma. 

What  is  the  post-mortem  rise  of  temperature  ? 

After  death  there  is  considerable  rise  of  the  temperature  of  the 
body,  which  is  very  marked  during  the  progress  of  rigor  mortis.  It 
may  amount  to  5°  or  10°  ¥.,  or  even  more. 

What  changes  occur  in  muscle  after  death? 

The  muscles  become  set  in  contraction,  and  their  reaction  becomes 
acid  from  the  development  of  lactic  acid. 

How  do  the  voluntary  muscles  act? 

They  act  as  the  power  which  moves  the  bones  in  their  function 
as  levers.  Each  of  the  three  classes  of  levers  is  illustrated  in  the 
body :  (1)  Fulcrum  between  power  and  weight :  ham-string  mus- 
cles acting  upon  the  ischium  to  raise  the  body  from  a  stooping 
position  ;  hip-joint,  fulcrum.  (2)  Weight  between  power  and  ful- 
crum :  depi'cssors  of  lower  jaw  acting  against  the  tension  of  the 
temporals,  etc.,  with  temporo-maxillary  articulation  for  fulcrum. 
(8)  Power  between  weight  and  fulcrum  :  biceps  of  the  arm  in 
raising  the  forearm,  with  elbow-joint  as  fulcrum. 

How  do  the  involuntary  muscles  act? 

They  do  not  have  attachments  to  the  hard  parts,  but  enter  into 
the  composition  of  the  walls  of  hollow  organs  which  require  elas- 
ticity and  variation  in  size.  The  heart  and  arteries,  as  well  the 
digestive  tract,  furnish  numberless  examples  of  their  action.  They 
are  often  rhythmical  in  their  action  (peristalsis),  and  the  stimula- 
tion of  this  class  of  muscles  does  not  cause  a  tetanus  (except  the 
heart),  but  a  succession  of  alternate  contractions  and  relaxations. 

NUTRITION. 
What  is  nutrition  ? 

By  nutriliun  we  mean  the  ])liysioliigical  principles  which  preserve 
the  normal  couditions  of  the  structure  and  fuuctiun  ol'  the  body,  so 


90  NUTEITION. 

far  as  refers  to  the  balance  between  the  income  and  outgo  of  mate- 
rial. While  it  is  almost  an  impossibility  to  study  this  subject  ex- 
actly, yet  an  idea  of  the  modes  of  expense  and  income  may  be 
gained  by  consideration  of  data  which  are  tolerably  fixed.  In  con- 
sidering the  income  and  expenditure  of  the  body  it  is  always  neces- 
sary to  bear  in  mind  that  all  the  factors  are  variable  and  the  results 
inconstant,  for  the  income  often  exceeds  the  expense,  and  vice  versa, 
in  life. 

What  are  the  daily  expenditures  of  the  body  ? 

The  more  important  are  those  by  the  ordinary  excretory  channels 
— lungs,  skin,  kidneys,  and  intestines. 

From  the  lungs  there  are  exhaled  every  twenty-four  hours — 

Of  carbonic  acid,  about 30  ounces. 

Of  water 10      "  40  ounces. 

Traces  of  organic  matter. 
From  the  skin — 

Water 23      " 

Solid  and  gaseous  matter 1  ounce.     24      " 

From  the  kidneys — 

Water 50  ounces. 

Organic  matter I2     " 

Minerals  and  salines ■    .    .       2  ounce.    52      " 

From  the  intestines — 

Water 4  ounces. 

Various    organic    and    mineral    sub- 
stances      2      "  6      " 

Total,  122  ounces. 

What  are  the  sources  of  income  ? 

Food  and  drink  and  oxygen  are  the  factors  of  the  income,  and 
may  be  calculated  about  as  follows  for  twenty-four  hours : 

Food  (chemically  dry) 16  ounces. 

Water  (as  drink  and  as  combined  with  solid  food)  .  80       "    • 
Oxygen  (absorbed  by  lungs) 26      " 

Total,  122  ounces. 

Thus  we  may  represent  the  schematic  plan  of  income  and  ex- 


NUTRITION.  91 

pensc  as  about  equal,  but  it  must   Ik-  borm;  in  mind  tbat  thu  iihiii 
(iiily  iv])ri'soiifs  an  average  result  i)f"  botli. 

How  are  variations  in  the  rate  of  income  and  expenditure  shown  ? 
By  (.'lianues  in  tlie  liodily  weiglit. 

What  is  the  result  of  the  expenditure  ? 

(1)  The  groicth  of  the  body  and  secretion  of  its  necessary  mate- 
rials, as  well  as  the  maintenance  of  the  tissues,  subjected  as  they 
are  to  the  wear  incident  to  the  continuance  of  life  and  function. 

(2)  The  continuance  of  physical  conditions  suitable  to  life  in  the 
form  of  heat  and  motion.  Tbe  actual  cimibustion  of  carbon  (/.  e.  oxi- 
dation) must  be  sufficient  to  maintain  the  animal  heat  and  the  nour- 
ishment of  the  muscles  upon  wliicli  tbe  continuance  of  Hie  dej)end. 

(8)  Nervous  energy,  as  in  the  regulation  of  all  physiological  pro- 
cesses by  the  reflexes,  as  well  as  in  voluntary  mental  and  nervous 
action. 

What  is  the  amount  of  energy  resulting  from  the  bodily  expend- 
iture? 

The  daily  work  of  the  body  has  been  calculated  to  be  about 
3400  foot-tons.  Of  this  about  one-tenth  has  been  considered  to  be 
exhausted  in  involuntary  muscular  action  (circulation,  respiration, 
etc.)  and  in  voluntary  motion,  while  the  remainder  (nine-tenths)  is 
expended  in  maintaining  the  body -heat.  Another  method  of  con- 
sidering this  enormous  force  may  be  of  use :  it  is  equivalent  in 
heat  to  that  required  to  raise  nearly  50  pounds  of  water  from  tbe 
freezing  to  the  boiling-point,  or  in  mechanical  force  it  is  sufficient 
to  raise  the  body  of  a  man  weighing  150  pounds  to  a  height  of  82 
miles. 

Does  this  calculation  include  all  the  energy  developed  in  the 
body? 

No.  It  takes  no  account  of  energy  exerted  in  nervous  manifes- 
tations, nor  does  it  take  into  consideration  the  utilization  of  the 
heat  absorbed  by  the  body. 

What  is  "nitrogenous  equilibrium"? 

Wlien  an  animal  is  fed  exclusively  upon  a  nitrogenous  diet,  it  is 
found  that  after  a  time  the  egested  nitrogen  approaches  and  finally 
balances  that  taken  in  as  food.     Tliis  is  known  as  tbe  "  nitrogenous 


92  NUTEITION. 

equilibrium."  But  at  the  same  time  the  animal  may  increase  in 
weight,  and  this  occurs  by  the  formation  of  fat  which  is  stored  up 
in  the  tissues.  The  nitrogenous  equilibrium  is  more  easily  main- 
tained by  the  addition  of  carbohydrates  to  the  food. 

What  is  the  eflfect  of  starvation  upon  the  body  ? 

There  is  a  loss  of  weight  in  all  the  tissues,  but  it  is  in  the  loss  of 
the  fat  that  the  change  is  most  marked :  the  fat  almost  entirely 
(93  per  cent.)  disappears  after  death  from  starvation.  The  sense 
of  hunger  gives  way  to  a  sense  of  pain  ;  thirst  is  excessive ;  sleep 
is  absent ;  progressive  weakness  accompanies  increasing  emaciation  ; 
the  exhalations  of  the  skin  and  lungs  are  foetid  ;  and  diarrhoea  with 
convulsions  or  delirium  often  precedes  death.  Death  occurs  with 
absolute  deprivation  of  both  food  and  drink  at  the  end  of  about  a 
week  (six  to  ten  days),  though  life  may  be  considerably  prolonged 
by  small  quantities  of  food  or  water.  The  temperature  of  the  body 
falls  before  death  very  considerably  (30°  C.),  and  it  has  been  con- 
sidered that  death  resulted  from  cold,  no  fuel  being  furnished  to 
maintain  animal  heat.  The  body  decays  rapidly  after  death  from 
starvation. 

What  is  the  effect  of  an  exclusive  diet  ? 

The  result  of  feeding  animals  exclusively  on  a  single  article  of 
diet  (sugar,  gum,  oil,  etc.)  is  practically  the  same  as  that  of  star- 
vation, except  that  death  does  not  occur  until  the  end  of  four  or 
five  weeks.  In  man  the  exclusive  diet  of  isolated  communities 
often  results  in  the  breaking  down  of  tissue  and  general  malnu- 
trition. 

What  is  the  effect  of  over-feeding  ? 

An  excess  of  nitrogenous  food,  if  digested,  increases  the  meta- 
bolic work  of  the  glandular  organs  (especially  of  liver  and  kidneys), 
and  induces  disease  in  those  organs  and  faulty  excretion  of  nitrog- 
enous matter.  This  may  be  obviated  or  delayed  by  active  physi- 
cal exercise.  Carbohydrate  food  in  excess  is  stored  up  in  the  form 
of  fat,  which  may  be  excessive,  with  resulting  fatty  infiltration  of 
the  viscera,  or  it  may  show  as  glycosuria. 

An  excess  of  any  food  is  apt  to  pass  undigested  through  the  intes- 
tines and  undergo   putrefactive  changes,  with  resulting  gaseous 


NERVOUS  SYSTEM.  93 

distension  :  the  carbohydrates  are  especially  apt  to  give  rise  to  this 
disturbance. 

What  are  the  requirements  of  a  normal  diet  ? 

There  should  bo  a  general  diet  of  well-cooked  food,  and  it  should 
contain  about  the  amount  of  carbon  and  nitrogen  which  is  excreted; 
tliat  is,  it  should  maintain  an  e(|uilibrium.  This  is.  commonly, 
about  two  pounds  of  solid  food  and  two  quarts  of  fluid.  The  pro- 
])ortion  of  the  various  kinds  of  foods  varies  considerably,  but  in  a 
general  way  for  a  healthy  man  one  may  divide  the  solid  food  some- 
what in  this  way  :  nitrogenous  food  (meat),  about  I  pound  ;  hydro- 
carbon and  fiit-food  (bread,  vegetables,  and  butter),  about  lo 
])ounds.  Besides  this,  the  food  will  contain  from  1  to  2  ounces 
of  salts  and  a  varying  amount  of  sugar. 

NERVOUS  SYSTEM. 

THE   NERVES. 

What  are  the  elementary  tissues  of  the  nervous  system  ? 

Nerve-fibres  and  nerve-cells.  The  fibres  are  of  two  kinds,  and 
are  united  in  bundles  to  form  nerve-trunks  or  nerves.  The  cells 
are  collected  in  groups  and  form  the  nerve-ganglia,  but  the  nerve- 
fibres  are  also  found  in  the  ganglia. 

What  varieties  of  nerve-fibres  occur  ? 

1,  The  medullated  or  white  fibres ;  2,  the  non-meduUated  or  gray 
fibres. 

Describe  the  medullated  or  white  fibres. 

1'liese  fibres  consist  of  an  external  nucleated  sheath  or  Pjo.  22. 
neurilemma  which  is  made  up  of  (1)  a  layer  (Fig.  22) 
of  endothelial  cells  which  surround  and  invest ;  and  (2) 
an  inner  protective  medidhiry  sheath  (the  white  matter 
of  Schwann).  Within  these  is  (3)  the  axis-cylinder, 
which  consists  of  a  number  of  the  primitive  fibrillae 
of  the  nervous  tissue.  In  size  these  fibres  vary  con- 
siderably, but  the  average  may  be  said  to  be  about 
Tr,Vu  ^"^^^  "1  diameter.  Diagram    of 

Structure  of 

What  are  the  nodes  of  Ranvier?  Nerve-tibre. 

They  are  constrictions  which  occur  here  and  there  in  the  course 


94 


JfEEVOUS  SYSTEM. 


of  the  white  fibres.     These  constrictions  (Fig.  23)  are  of  the  ex- 
ternal sheath,  and  break  the  continuity  of  the 
Fig.  23.  medullary  layer. 

Is  the  axis-cylinder  broken  at  the  nodes  of  Ran- 
vier? 

No.  The  axis-cylinder  is  continuous  from  one 
end  of  the  nerve-fibre  to  the  other. 

Describe  the  non-meduUated  fibres. 

They  consist  of  the  axis-cylinder  alone,  with- 
out the  medullary  layer.  They  do  not  differ  in 
any  other  regard  from  the  white  fibres.  When 
collected  in  bundles  to  form  nerves  they  have  a 
yellowish  or  grayish  color.  They  are  found  in 
the  olfactory  and  auditory  nerves  and  in  the 
nerves  of  the  sympathetic  system,  and  they  occur 
in  greater  or  less  number  in  the  nerves  of  the 
cerebro-spinal  system.  In  size  these  fibres  are 
about  one-third  to  one-half  the  diameter  of  the 
medullated.  They  are  sometimes  spoken  of  as 
the  fibres  of  Remah. 

What  change  occurs  to  the  white  fibres  near 
their  termination? 

The  medullary  layer  disappears  and  the  axis- 
cylinder  continues  with  the  neurilemma  ;  but  this 
too  disappears  before  the  final  ending  of  the  fibre 
in  the  tissues.  The  fibre  then  splits  into  two  or 
more  terminal  branches ;  that  is,  the  white  fibre 
becomes  a  non-medullated  fibre. 


^r— - 


Nerve-fibre  from  the 
Sciatic  Nerve  of  the 
Rabbit,  after  the  ac- 
tion of  nitrate  of  sil- 
ver :  a,  ring  formed 
by  thiclvened  mem- 
brane of  Schwann ; 
TO,  wliite  substance 
of  Schwann  render- 
ed transparent  by 
glycerin ;  cy,  cylin- 
der-axis, which  just 
above  and  below  the 
level  of  the  annular 
constriction  p  r  e  - 
sents  the  striae  of 
Frommann. 


How  are  the  fibres  united  to  form  nerves? 

The  fibres  are  joined  in  bundles  which  are 
enclosed  in  a  thin  fibrous  sheath  (perineurium),  and  these  bundles 
of  nerve-fibres  are  bound  in  a  firm  connective  tissue  which  serves 
to  protect  and  to  unite  them  strongly. 

What  are  the  characteristics  of  nerve-cells  ? 

Nerve-cells  or  ganglion-cells  present  a  great  variety  of  shapes, 
and  yet  have  common  characteristics.  The  cell-body  is  granular 
and  contains  a  large  nucleus  which  contains  a  prominent  nucleolus. 
The  cells  have  at  least  one  process,  and  often  more  (Fig.  24).  and 


THE   NERVES.  95 

the  cells  are  classified  as  unipolar,  bipolar,  or  multipolar.  These 
])rocesses  are  of  two  kinds — one  kind  dividing  and  subdividing 
i^hninchiii(/  ju-ocL'sscs)  until  they  become  very  delicate  and  seem  to 

Fig.  24. 


Nerve-cells  from  the  Anterior  Horn  of  Gray  Substance  of  the  Spinal  Cord. 

join  with  the  equally  fine  processes  from  other  cells ;  another  class 
(^(t.rii>-ci/h'niler  processes')  pass  on  without  division,  and  become  axis- 
cylinders  of  medullated  nerve-fibres. 

The  nerve-cells  vary  greatly  in  size,  and  arc  very  diverse  in 
form,  but  the  presence  of  nucleus  and  nucleolus  and  of  the  pro- 
cesses is  characteristic  of  nerve-cells.  They  may  be  enclosed  in  a 
delicate  capsule  which  becomes  continuous  with  the  neurilemma 
(Fig.  25). 

What  is  the  function  of  the  nerve-fibres  ? 

The  transmission  of  a  stimulus.  The  axis-cylinder  connects 
the  centre  and  periphery  cells,  and  conveys  between  them  the 
stimuli.  This  transmission  for  any  particular  fibre  is  in  one  direc- 
tion only. 

How  may  the  nerve-fibres  be  classified? 

Into  afferent  (or  centripefitf)  and  efferent  (or  centrifugal)  fibres. 


96 


NERVOUS  SYSTEM. 
Fig.  25. 


Nerve-cells,  from  Spinal  and  Sympathetic  Ganglia  of  Man,  enclosed  in  their  Capsular 
Sheaths — from  hardened  preparations  (Key  and  Eetzius). 

The  former  are  those  by  which  impressions  are  taken  from  the 
periphery  to  the  brain,  and  are  commonly  called  sensory  fibres. 
The  latter  conduct  the  stimuli  to  the  periphery,  and  are  known 
as  motor  fibres.  Besides  these,  some  of  the  fibres  serve  to  connect 
ganglia  of  the  central  system  one  with  another,  and  these  are 
known  as  intereentral  fibres. 

What  modifications  of  function  belong  to  the  afferent  nerves  ? 

The  direct  function  of  the  centripetal  nerves  is  the  conduction 
of  an  impulse  which  gives  rise  to  a  sensation,  as  of  pain  or  heat; 
but  beyond  this  we  may  have  a  reflex  or  an  inhibitory  impulse 
conducted. 

What  modifications  of  function  belong  to  the  efferent  nerves? 
The  centrifugal  nerve-fibres  may  carry  other  than  motor  im- 


THE   NERVES.  97 

pulses :  they  control  nutrition  (trophic  nerves)  and  secretion 
(secretory  nerves),  and  they  may  also  increase  or  check  other 
etlorent  impulses. 

What  is  the  velocity  of  the  transmission  of  impulses  ? 

Kftcreut  impulses  are  somewhat  slower  than  atlerent.  the  rate 
for  the  former  being  about  llU  feet  per  second,  for  the  latter 
about  150  feet. 

What  are  "personal  error"  and  "personal  equation"? 

The  time  occupied  in  executing  a  voluntary  movement  at  a  given 
signal — for  instance,  the  recording  the  time  of  a  transit  in  an  astro- 
nomical observation — is  found  to  be  sufficient  to  demand  a  correction 
for  an  accurate  result.  This  amounts  to  i  to  -^^  of  one  second  with 
different  individuals.  The  time  lost  in  this  Avay  is  known  as  the 
/x'rsoita/  error  of  the  observer.  When  this  has  been  ascertained 
by  experiment,  the  allowance  to  be  made  for  the  personal  error  is 
his  personal  equation.  This  remains  nearly  constant  for  each 
person. 

How  do  the  sensory  nerves  terminate  at  the  periphery? 

The  sensory  nerves  ending  in  the  skin  find  their  way  to  certain 
bodies  (sense-organs)  which  are  essential  to  the  conduction  of  the 
sensory  impression  to  the  central  nerve-ending.  These  sense- 
organs  are  of  several  kinds.  In  the  fingers  and  toes  are  found 
two  kinds  of  sense-organs  which  may  be  especially  mentioned  : 
1,  touch-corpuscles;  2,  Pacinian  corpuscles.  The  anatomy  and 
physiological  use  of  these  bodies  are  still  somewhat  obscure ; 
and,  indeed,  the  whole  subject  of  sensory  nerve-terminations  is 
but  illy  understood.  We  may  regard  the  fibres  of  sensory  nerves, 
as  a  majority,  to  form  a  minute  plexus  in  the  corium  and  to  ter- 
minate in  sense-organs  in  a  way  not  known.  Some  of  the  special 
sense-organs  are  possessed  of  nerve-endings  which  are  more  clearly 
observed. 

What  two  sets  or  systems  of  nerves  do  we  possess  ? 
The  cerebro-spinal  and  sympathetic. 

What  constitutes  the  cerebro-spinal  system? 

The  brain,  tlu;  niedulla  oblongata,  and  the  spinal  cord,  with  the 
nerves  proceeding  from  them. 

What  constitutes  the  sympathetic  system? 

Primarily,  the  sympathetic  system  consists  of  a  double  chain  of 
7— Phy. 


98  NERVOUS   SYSTEM. 

ganglia  and  communicating  nerves  whicli  lie  on  either  side  of  the 
vertebral  column  and  extend  throughout  its  entire  length.  Other 
ganglia  occur  in  connection  with  some  of  the  cranial  nerves,  more 
especially  the  vagus  and  trigeminus.  There  are  ganglia  and  plex- 
uses connected  with  the  various  organs  (e.g.  cardiac  and  solar),  and 
still  others  in  the  substance  of  some  of  the  organs  (e.  g.  stomach  and 
intestines).  The  sympathetic  system  has  numerous  communications 
with  the  cerebro-spinal  system. 

What  is  a  reflex  action? 

An  action  which  results  from  a  centripetal  nerve-impulse  passing 
to  a  nerve-centre  in  a  ganglion,  and  there  transforming  to  a  centrifu- 
gal impulse  passing  to  a  muscle.  Such  an  action  may  be  simple  and 
involve  a  single  muscle,  or  complex  and  involve  many  :  thus,  a  ray 
of  light  falling  upon  the  retina  causes  a  simple  reflex  contraction  of 
a  single  muscle,  and  the  iris  contracts.  As  an  illustration  of  a  com- 
plex reflex  action,  however,  irritation  of  the  larynx  causes  not  only 
a  closing  of  the  glottis,  but  a  contraction  of  all  the  muscles  involved 
in  forced  expiration  or  coughing. 

Are  all  reflex  actions  involuntary? 

Yes,  but  many  of  them  may  be  checked  or  prevented  by  a  vol- 
untary effort. 

Do  the  reflexes  depend  upon  the  cerebro-spinal  nervous  system 
or  upon  the  sympathetic? 

They  are  more  noticeable  in  the  cerebro-spinal  system,  but  they 
may  belong  to  either,  or  may  be  mixed,  the  impulse  going  by  the 
one  system  and  returning  by  the  other.  Examples :  sneezing, 
coughing,  swallowing  are  cerebro-spinal  reflexes ;  the  vaso-motor 
reflexes  are  largely  sympathetic,  but  the  centripetal  nerve  is  often 
cerebro-spinal,  as  in  the  secretion  of  saliva  or  in  blushing. 

What  relations   exist  between  the  stimulus  and  the  resulting 
reflex  ? 

A  stimulus  which  is  mild  causes  a  reflex  of  the  muscle  of  the 
same  side,  but  as  the  stimulus  is  increased  the  muscles  of  the  op- 
posite side  may  be  involved,  the  reflex  of  the  irritated  side  remain- 
ing the  stronger.  As  the  irritation  is  increased  the  reflex  involves 
more  muscles  ;  that  is,  the  stimulus  spreads  to  a  greater  number 
of  cells  in  the  ganglion  and  more  efferent  fibres  are  involved. 
These  relations  are  obtained  largely  by  experiments  upon  decap- 
itated frogs. 


SYMPATHETIC  SYSTEM.  99 

Wliat  are  acquired  reflex  actions  ? 

A  reflex  action  which  is  as  strong  in  an  infant  as  in  an  adult 
(the  contraction  of  the  pupil  in  the  presence  of  light)  is  a  prirnnry 
reflex.  Another  class  of  reflex  actions  re(juirc  frecjuent  repetition 
before  they  are  automatically  performed,  and  such  actions  arc  called 
acquired  reflex  actions,  as  walking,  reading,  etc. 

What  is  automatic  action  of  nerve-centres  ? 

There  are  certain  actions  which  continue,  and,  while  they  are 
closely  related  to  reflex  action,  do  not  seem  to  be  reflexes,  but  to 
originate  in  the  part.  Thus,  the  peristaltic  action  of  the  alimentary 
tract  is  not  dependent  upon  the  presence  of  food  in  the  intestines, 
but  may  be  excited  in  the  absence  of  food  or  checked  when  it  is 
present.  The  action  has  been  referred  to  small  ganglia  and  nerve- 
plexuses  found  there  (Auerbachs  and  Meissner's),  and  is  consid- 
ered to  originate  in  the  local  nerve-centres.  This  is  what  is  known 
as  automatism  or  automatic  nerve-action. 

What  power  of  inhibition  and  augmentation  of  action  has  the 
nerve-centres  ? 
In  speaking  of  the  action  of  the  heart  it  was  .shown  that  certain 
fibres  of  the  vagus  nerve  check  the  hearts  action,  and  certain 
other  fibres  increase  it.  This  control  of  the  action  of  organs  is 
not  confined  to  the  heart,  but  similar  power  of  regulation  belongs 
to  the  nervous  centres  for  many  other  organs. 

SYMPATHETIC    SYSTEM. 
How  is  the  sympathetic  nervous  system  arranged? 

It  is  arranged  in  ganglia  and  plexuses.  It  is  intimately  con- 
nected with  the  cerebro-spinal  system  by  communicating  branches 
from  each  spinal  nerve  and  many  of  the  ci'anial  nerves. 

What  is  a  ganglion  ? 

It  is  a  collection  of  gray  and  white  nerve-substance,  which  is 
usually  oval  in  outline,  and  is  frequently  found  in  the  course  of  a 
nerve-trunk.  In  the  sympathetic  system  the  ganglia  contain 
numerous  nerve-cells,  smaller  than  those  of  the  brain  and  spinal 
cord,  and  from  these  cells  arise  nerve-fibres  which  distribute  them- 
selves in  the  plexuses. 

What  peculiarities  have  the  fibres  of  the  sympathetic  nerve  ? 
They  are  often  smaller  than  those  of  the  cerebro-spinal  .system, 


100  NERVOUS   SYSTEM. 

and  there  are  in  the  nerves  a  considerable  number  of  non-medul- 
lated  fibres — more  than  in  the  spinal  nerves. 

Do  the  sympathetic  nerves  differ  materially  from  the  cerehro- 
spinal  ? 

No.  They  are  very  similar.  The  occurrence  of  ganglia  upon 
the  sensory  branch  of  the  spinal  nerves  and  upon  the  sensory  cra- 
nial nerves  (pneumogastric,  glosso-pharyngeal,  and  trigeminus)  adds 
to  the  similarity.  Then,  too,  the  frequent  communications  be- 
tween the  two  systems  practically  makes  one  system  of  them,  and 
the  division  is  largely  one  for  convenience. 

Is  the  sympathetic  system  dependent  upon  its  connection  with 
spinal  axis? 

Yes. 

Where  are  the  functions  of  the  sympathetic  system  most  shown  ? 
In  the  organs  of  nutrition   and  secretion  and  in   the  vascular 
system. 

What  are  the  sympathetic  ganglia  in  the  head? 

They  are  four  in  number — ophthalmic,  spheno-palatine,  submax- 
illary, and  otic  ganglia.  Each  has  communications  from  the  gen- 
eral sympathetic,  and  from  the  cranial  nerves  both  motor  and  sen- 
sory fibres. 

Describe  the  ophthalmic  ganglion. 

It  is  a  small  ganglion  situated  in  the  orbit,  and  receives  com- 
munications' from  the  sympathetic  and  from  the  motor  oculi 
(third)  nerve,  a  motor  branch,  and  from  the  trigeminus  (fifth) 
nerve  a  sensory  branch.  Its  branches  pass  into  the  eyeball  (ciliary 
nerves),  and  are  distributed  in  the  iris.  Their  function  is  the  con- 
trol of  the  pupil,  of  the  apparatus  of  accommodation,  and  of  the 
vaso-motor  function  in  the  vessels  of  the  eye. 

Describe  the  spheno-palatine  ganglion. 

It  is  situated  in  the  spheno-maxillary  fossa,  and  receives  branches 
from  the  cervical  sympathetic  system  and  motor  fibres  from  the 
facial  (seventh)  nerve,  and  sensory  from  the  fifth.  Its  branches  are 
distributed  to  the  mucous  membrane  and  muscles  of  the  palate 
and  uvula,  and  to  the  naso-pharynx.  They  are  both  sensory  and 
motor. 


SYMPATHETIC  SYSTEM. 

Fi<;.  2G. 


101 


Ganglia  and  Nerves  of  the  Sympathetic  System. 

Describe  the  submaxillary  ganglion. 

It  lies  in  close  proximity  to  the  submaxillary  glaud.     It  receives 


102  NERVOUS   SYSTEM. 

branches  from  the  superior  ganglion  of  the  neck  and  a  sensory 
branch  from  the  lingual  branch  of  the  fifth  nerve.  Its  motor  branch 
is  through  the  chorda  tympani  nerve  from  the  seventh  or  facial 
nerve.  Its  branches  are  distributed  to  the  submaxillary  gland  and 
control  its  function. 

Describe  the  otic  ganglion. 

It  is  a  small  ganglion  lying  upon  the  third  division  of  the  fifth 
nerve  as  it  emerges  from  the  foramen  ovale.  It  has  branches  from 
the  sympathetic  on  the  middle  meningeal  artery,  and  both  a  motor 
and  a  sensory  communication  from  the  fifth,  as  well  as  a  branch  from 
the  glosso-pharyngeal  through  Jacobson's  nerve.  Its  branches  are 
motor,  to  the  tensor  palati  and  tensor  tympani  muscles  ;  and  sensory, 
to  the  mucous  membrane  of  the  tympanum  and  Eustachian  tube. 

How  does  the  sympathetic  system  in  the  trunk  communicate 
with  the  spinal  nerves  ? 
From  each  spinal  nerve  is  given  off  a  communicating  branch  to 
a  neighboring  ganglion.     These  branches  contain  both  motor  and 
sensory  fibres. 

How  are  the  ganglia  classified? 

Into  cervical,  thoracic,  abdominal,  and  pelvic  ganglia  and 
plexuses. 

Describe  the  cervical  ganglia. 

There  are  two — a  superior  and  inferior  (with  sometimes  a  third, 
middle) — ganglia  on  each  side  (Fig.  26).  These  ganglia  receive 
communications  from  each  of  the  cervical  spinal  nerves  and  from 
each  other.  Their  branches  are  given  off  to  form  (1)  the  carotid 
plexus,  which  follows  the  carotid  artery  and  its  branches.  It  forms 
by  its  inosculations  the  vaso-motor  plexuses  of  the  arterial  system, 
and  furnishes  branches  for  distribution  to  the  thyroid  gland,  larynx, 
trachea,  pharynx,  and  oesophagus.  (2)  It  furnishes  the  cardiac 
nerves,  which  are  distributed  in  the  cardiac  plexus. 

"What  is  the  distribution  of  the  thoracic  ganglia? 

In  the  chest  the  ganglia  are  numerous  (Fig.  26),  and  each  gan- 
glion receives  two  branches  of  communication  from  the  intercostal 
nerve  above  it,  while  the  relationship  of  the  ganglia  is  maintained 
by  the  intercommunicating  chain.  The  nerves  originating  here 
are  distributed  to  the  plexuses  on  the  thoracic  aorta,  and  to  those 
of  the  lungs  and  oesophagus. 


SYMPATHETIC  SYSTEM.  103 

Describe  the  abdominal  sympathetic. 

In  the  alxlunn'ii  the  sympathetic  consists  mainly  of  an  aggrega- 
tion of  ganglionic  enlargements  situated  upon  the  coeliac  artery, 
known  as  the  semilunar  or  coeliac  ganglion.  It  communicates  with 
the  thoracic  ganglia  and  with  all  the  lumbar  nerves.  From  this 
centre  proceed  a  multitude  of  diverging  and  inosculating  fibres, 
which,  from  their  common  origin  and  radiating  course,  are  called 
the  aolar  phwun.  Its  secondary  plexuses,  accompanying  the  branches 
of  the  abdominal  aorta,  are  distributed  to  the  stomach,  intestines, 
spleen,  pancreas,  liver,  kidney,  and  internal  organs  of  generation. 

How  are  the  pelvic  plexuses  derived? 

From  four  or  tive  pairs  of  ganglia  situated  on  the  anterior  por- 
tion of  the  sacrum  and  terminating  in  the  gnnglioti  I'mjxir,  lying 
upon  the  coccyx.  Its  fibres  join  those  from  the  solar  plexus,  and 
are  distributed  with  them  along  the  course  of  the  branches  of  the 
internal  iliac  arteries. 

Describe  the  sensibility  and  motor  influence  of  the  sympathetic 
nerves. 

It  will  be  remembered  that  the  spinal  nerves,  both  afferent  and 
efferent,  act  very  quickly  upon  the  tissues  supplied  by  them  ;  the 
sympathetic  nerves  act  more  slowly.  Thus,  if  the  afferent  nerve 
or  a  ganglion  or  its  efferent  nerve  be  stimulated,  there  is  a  slow 
wave-like  series  of  motions  set  up  in  the  parts  supplied,  which  con- 
tinue for  some  time  after  the  stimulus  is  withdrawn.  This  is  par- 
ticularly Avell  seen  in  the  intestinal  peristalsis  which  may  be  excited 
by  stimulation  of  the  intestine  or  of  the  semilunar  ganglion  or  of 
the  branches  of  the  solar  plexus. 

What  is  the  effect  of  the  sympathetic  nerves  upon  special  senses  ? 

The  dilatation  of  the  pupil  is  effected  through  it,  and  probably 
the  accommodation  is  acted  xxpon  by  fibres  other  than  the  oculo- 
motorius,  which  come  through  the  lenticular  ganglion.  The  tensor 
tympani  muscle  is  supplied  from  the  otic  ganglion. 

What  is  the  vaso-motor  function  of  the  sympathetic  ? 

The  muscular  coats  of  the  lilood-vessels.  especially'  of  the  arteries, 
are  under  the  control  of  the  sympathetic  filaments  and  plexuses, 
which  accompany  them  throughout  their  entire  system.  These 
fibres  are  of  two  kinds  as  regards  their  function  :  (1)  vaso-con- 
strictor  and  (2)  vaso-dilator  fibres. 


104  NERVOUS   SYSTEM. 

How  do  the  vaso-motor  fibres  arise? 

They  probably  arise  from  spinal  centres,  and  are  controlled  in 
some  way  by  the  vertebral  ganglia  of  the  sympathetic  system. 
The  vaso-dilator  fibres  are  not  to  be  distinguished  as  such,  though 
their  presence  is  inferred  from  the  action  of  special  nerves.  Eor 
example,  the  stimulation  of  the  chorda  tympani  nerve  has  a  vaso- 
dilator effect  in  the  submaxillary  gland.  The  inhibitory  and  aug- 
mentary  eifects  of  the  cardiac  nerves  are  similarly  carried  by  or 
through  sympathetic  plexuses. 

Do   the   visceral   sympathetic    nerves  have   a   similar   central 
origin  ? 

Yes,  but  they  too  are  acted  upon  by  the  ganglia  through  which 
the  fibres  pass,  and  in  which  new  nerves  arise  from  the  nerve-cells. 

What  control  has  the  sympathetic  system  over  the  secreting 
glands  ? 
There  has  been  demonstrated  in  some  of  the  secreting  glands — 
and  it  is  probably  true  for  all — that  functional  stimuli,  distinct 
from  the  vaso-motor,  come  through  the  sympathetic  nerves,  and 
that  these  fibres  are  closely  associated  with  the  vaso-motor  fibres. 
Thus,  in  the  stomach  the  secretion  of  the  gastric  juice  is  only  tem- 
porarily suspended  by  the  section  of  the  vagi,  and  is  resumed  by 
the  action  of  the  sympathetic,  showing  that  the  control  is  by  the 
sympathetic. 

What  is  "  arrest  of  action  "  ? 

It  is  a  temporary  check  upon  the  control  of  an  organ  by  the 
sympathetic  system,  which  check  comes  through  the  cerebro-spinal 
system.  Such  an  action  is  frequent  in  the  control  of  the  glandular 
organs,  and  usually  is  shown  in  the  dilatation  of  the  capillaries 
through  the  arrest  of  the  action  of  the  vaso-motor  nerves  in  response 
to  a  sensory  reflex.  It  is  also  seen  in  the  sphincters,  which  keep 
up  a  condition  of  tonic  contraction  to  close  the  orifices  of  the  body, 
but  relax  in  response  to  an  impulse  from  the  proper  centre.  The 
sphincter  ani  in  this  way  retains  its  hold  upon  the  intestinal  orifice 
until  the  centre  in  the  cord  permits  an  arrest  of  action  and  relaxa- 
tion of  the  muscle. 

SPINAL  CORD. 
Describe,  roughly,  the  spinal  cord. 

The  spinal  cord  is  that  portion  of  the  cerebro-spinal  nervous  sys- 


SPINAL  CORD. 


105 


tern  contained  within  the  spinal  canal.  It 
connects  with  the  brain  through  the  medulla 
oblongata,  and  terminates  in  a  fine  thread  of 
gray  matter  (the  filum  termiiiale)  at  about 
the  second  lumbar  vertebra.  In  form  it  is 
irregularly  cylindrical,  and  varies  in  the  size 
and  shape  of  its  cross-section  at  various  lev- 
els, as  is  shown  in  Fig.  27.  It  is  incom- 
pletely divided  into  symmetrical  halves,  and 
its  mid-line  is  indicated  in  front  by  a  fissure 
(anterior  median  fissure)  which  extends  for 
about  one-third  its  antero-posterior  diameter  ; 
behind  by  a  deeper  but  narrower  fissui'c  (pos- 
terior median  fissure),  which  involves  about 
one-half  of  the  same  diameter.  It  is  com- 
posed of  white  and  gray  substance. 

How  are  the  white  and  gray  matters  ar- 
ranged in  the  spinal  cord? 

The  white  substance  is  arranged  externally 
to  the  gray  in  each  half  of  the  cord,  and  is 
so  dispo.sed  as  to  be  conveniently  divided  for 
purposes  of  description  into  three  columns, 
known  respectively  as  the  anterior,  lateral, 
and  posterior  columns  of  the  cord.  There  is 
also  a  thin  band  of  white  substance  at  the 
base  of  the  anterior  median  fissure  (the  white 
commissure).  The  gray  matter  fills  in  the 
central  portion  of  the  cord,  and  is  variable  in 
its  amount,  the  calibre  of  the  cord  at  its  en- 
largements being  increased  by  the  increase 
in  the  amount  of  gray  matter  at  these  points 
(Fig.  27).  The  white  substance  will  be  no- 
ticed to  diminish  quite  regularly  in  the  sec- 
tions of  the  cord  from  above  downward,  as 
seen  in  this  .series.  The  gray  substance  is  not 
completely  halved  by  the  anterior  and  pos- 
terior fissures  of  the  cord,  but  is  continuous 
across  the  mid-line ;  and  in  it  at  the  centre 
is  a  minute  canal  communicating  with  the 
ventricles  of  the  brain.  The  gray  matter  is 
more  abundant  between  the  lateral  and  anterior  and  between   the 


Transverse  Sect  ions  of  the 
.Si)inal  (,"ord  in  .Man:  I, 
upi)pr    cervical    region ; 

II,  lower  cervical  region; 

III,  dorsal  region;  IV, 
lumbar  enlurgeuient ;  V, 
lower  extremity. 


106 


NERVOUS  SYSTEM. 


Transverse  Section  of  the  Spinal  Cord  :  n,  h, 
spinal  nerves  of  right  and  left  'sides; 
d,  origin  of  anterior  root;  e,  origin  of  pos- 
terior root ;  c,  ganglion  of  posterior  root. 


lateral  and  posterior  columns  of  the  white  substance,  and  the  names 
anterior  and  posterior  horns  (cornua)  are  given  to  these  regions 
respectively. 

What  are  the  nerve-roots  of  the  cord  ? 

Issuing  from  the  cord  along  its  course  are  thirty-one  pairs  of 
nerves.     Each  of  these  spinal  nerves  is  made  up  of  an  anterior  and 

a   posterior   root  (Fig.  28),  of 
Fig.  28.  which  the  latter  is  the  larger. 

The  anterior  root  arises  between 
the  anterior  and  lateral  white 
columns,  the  posterior  between 
the  posterior  and  lateral  col- 
umns. On  each  posterior  nerve- 
root  is  found  a  ganglion  imme- 
diately beyond  its  point  of 
emergence.  The  function  of 
this  seems  to  be  trophic. 

What  is  the  minute  structure  of  the  white  substance  ? 

It  is  found  to  be  made  up  of  medullated  nerve-fibres,  which 
collect  to  form  the  anterior  and  posterior  nerve-roots,  and  commu- 
nicate with  other  regions  of  the  cord. 

What  is  the  minute  structure  of  the  gray  matter  ? 

The  gray  matter  contains  multipolar  cells  of  varying  size  and 
shape,  with  axis-cylinders  and  "  branching "  processes  lying  in 
the  neuroglia  (connective  tissue).  The  multipolar  cells  are  some 
of  them  quite  large.  In  the  anterior  horn  of  the  gray  substance 
the  axis-cylinder-processes  of  the  nerve-cells  connect  directly  with 
fibres  forming  the  anterior  nerve-roots  (Fig.  29)  ;  but  in  the  poste- 
rior cornu  the  communication  is  through  the  branching  processes 
joining  the  divided  axis-cylinders  of  the  posterior  nerve-roots,  form- 
ing thus  a  minute  plexus  known  as  Gerlach's  nerve-network. 

Whence  are  the  fibres  derived  which  make  up  the  nerve-roots  ? 

(a)  Anterior  nerve-roots  are  derived  from  (1)  the  anterior  col- 
umns of  the  cord,  but  some  fibres  come  through  the  commissure 
from  (2)  the  opposite  side,  and  some  come  from  (3)  the  lateral 
tract.  Still  other  fibres  arise  from  (4)  the  multipolar  cells  in  the 
anterior  cornu  of  the  gray  matter.  The  fibres  of  the  anterior 
nerve-roots  are  efferent  or  motor  fibres. 


SPINA  I,   (T)Un. 


107 


(A)  Posterior  nerve-roots  enter  into  the  posterior  horn  of  the 
gray  matter,  and  the  fibres  break  up  to  form  Gcrlach's  network, 
communicating  with  the  large  multipolar  cells,  but  some  fibres 


Fig.  29. 


Transverse  Section  of  the  Spinal  Cord  in  Man  (lumbar  region). 

cross  through  the  gray  commissure  to  the  opposite  side.     The  fibres 
of  the  posterior  roots  arc  aft'crent  or  sensory  fibres. 

If  the  anterior  nerve-roots  be  cut,  what  is  the  result  ? 

The  anterior  nerve-roots  are  efferent  or  motor ;  therefore  their 
divi.sion  results  in  complete  loss  of  motion  in  the  parts  supplied. 
If  the  distal  portion  of  the  cut  nerve-root  be  stimulated,  muscular 
action  follows,  while  irritation  of  the  proximal  portion  produces  no 
noticeable  effect. 

What  follows  division  of  the  posterior  roots  ? 

Loss  of  sensation  without  loss  of  motion.  Stimulation  of  the 
distal  portion  of  the  cut  posterior  root  produces  no  result,  either 
in  sensation  or  motion.  Irritation  of  the  proximal  end  will,  how- 
ever, cause  very  acute  pain. 

Is  the  course  of  the  fibres  through  the  spinal  cord  known  ? 
No,  not  fully.     Certain  fibres  have  been  traced  with  fair  accu- 


108 


NERVOUS   SYSTEM. 


racy  through  their  length,  notably  fibres  to  the  arm  (direct  pyra- 
midal tract)  in  the  anterior  column,  and  to  the  leg  (crossed  pyra- 
midal tract)  in  the  lateral  column. 

Do  all  the  fibres  of  the  spinal  nerves  pass  from  the  brain  through 
the  spinal  cord? 

No.  It  has  been  calculated  that  only  about  one-half  as  many 
fibres  enter  the  spinal  cord  from  the  brain  as  leave  it  through  the 
nerves  ;  therefore  it  must  follow  that  some  fibres  originate  from  the 
cord.  The  increase  in  gray  matter  in  the  cervical  and  lumbar  enlarge- 
ments, where  the  fibres  for  the  large  plexuses  of  the  nerves  (brach- 
ial and  lumbar)  are  given  ofi",  confirms  this  view. 

Where  are  the  trophic  centres  for  the  anterior  nerve-roots  ? 

The  posterior  nerve-roots,  we  have  seen,  seem  to  be  dependent 
upon  the  ganglia  which  are  found  upon  them  for  trophic  influence. 
The  anterior  root  in  a  similar  way  seems  to  depend  upon  a  trophic 
centre  in  the  gray  matter  in  the  anterior  horn. 

What  is  degeneration  of  a  nerve-fibre  ? 

Division  of  a  nerve  is  followed  by  a  degeneration  or  breaking 
down  of  the  axis-cylinders  of  its  fibres  within  a  day  or  two,  the 
loss  of  function  being  an  earlier  and  immediate  manifestation.    This 


Fig.  30. 


Degeneration  of  Spinal  Nerves  and  Nerve-roots  after  Section  :  A,  section  of  nerve-trunk 
beyond  the  ganglion;  B,  section  of  anterior  root;  C,  section  of  posterior  root;  D, 
excision  of  ganglion  ;  a,  anterior  root ;  p,  posterior  root ;  g,  ganglion. 

degeneration  is  centrifugal ;  that  is,  does  not  proceed  toward  the 
spine,  but  to  the  periphery.  If  the  posterior  root  be  cut,  how- 
ever, between  its  ganglion  and  its  emergence  from  the  cord,  the 
degeneration  is  toward  the  cord — i.  e.  centripetal — and  the  nerve 


SPINAL   CORD.  109 

beyond  the  ganglion  does  not  degenerate.  The  anterior  root  can- 
not, however,  be  divided  at  any  l><»iiit  beyond  its  emergence  without 
centrifugal  degeneration  of  the  fibres  (Fig.  30).  The  regeneration 
takes  place  slowly  if  the  continuity  of  the  nerve  is  at  once  restored, 
and  may  even  follow  after  the  nerve  has  degenerated  for  some  months 
and  a  complete  loss  of  function  has  affected  the  part  supplied  by 
it.  The  fact  that  the  axis-cylinders  are  restored  only  in  this  way 
is  of  interest,  as  showing  the  influence  of  the  trophic  centres  on 
the  nerve-growth. 

What  are  the  functions  of  the  spinal  cord  ? 

(1)  The  conduction  of  impulses  from  the  nerves  to  the  brain 
and  from  brain  to  nerves,  and  (2)  the  origination  of  action  in 
response  to  stimuli  from  the  periphery — i.  e.  rcjicx  action. 

Explain  the  action  of  the  cord  as  a  conductor  of  nervous  impulses. 
Than  by  the  spinal  cord  there  is  practically  no  other  nervous 
communication  between  the  brain  and  the  musciilo-cutaneous  sys- 
tem ;  hence  through  it  must  come  all  the  nerve-impulses  which 
pass  to  or  from  the  brain.  In  other  words,  every  sensory  impulse 
that  is  felt  and  every  motion  that  is  iriUcd.  perception  and  volition 
being  attributes  of  the  brain,  must  be  conducted  through  the  nerve- 
fibres  of  the  spinal  cord  to  the  brain,  and  vice  versa.  No  better  illus- 
tration need  be  used  than  the  abolition  of  both  motor  and  sensory 
function  which  follows  a  cerebral  apoplexy  :  the  nerve-centre  being 
destroyed,  voluntary  action  and  perception  of  sensation  are  lost, 
and  yet  the  reflex  response  is  prompt,  showing  that  the  brain- 
function  is  necessary  in  the  chain  of  phenomena.  Again,  the 
same  paralysis  follows  the  section  of  the  cord,  and  we  must 
acknowledge  their  mutual  dependence. 

Does  the  gray  substance  act  as  conductor? 

No,  not  when  directly  stimulated.  The  conducting  fibres  seem 
to  be  in  the  white  columns,  and  each  portion  contains  fibres  which 
always  conduct  the  same  kind  of  impression. 

What  is  the  course  of  sensory  impulses  in  the  spinal  cord  ? 

This  is  somewhat  pniljloniatical,  but  certainly  these  impulses 
enter  the  cord  by  the  posterior  nerve-roots.  The  fibres  conducting 
them  break  up  to  form  Gerlachs  network,  and  cross  to  the  opposite 
side  of  the  cord  through  the  gray  commissure.  It  is  probable  that 
after  decussating  the  fibres  communicate  with  multipolar  cells,  and 


110  NERVOUS  SYSTEM. 

thus  pass  on  as  white  fibres  in  the  lateral  columns.  These  fibres 
enter  the  lateral  columns  (of  the  opposite  side),  and  pass  to  the 
medulla  as  a  distinct  tract — the  antero-lateral  ascending  tract — at 
the  periphery  of  the  lateral,  extending  into  the  anterior  column. 

What  sensations  are  transmitted  by  this  set  of  fibres  ? 

It  is  by  this  tract  that  sensations  of  pain  and  of  temperature  are 
supposed  to  pass.  There  are  also  afi"erent  fibres  in  the  posterior 
columns — the  posterior  median — by  which  the  sensations  of  touch 
and  toeigJit  (or  muscular  sensation)  are  believed  to  pass ;  the  latter, 
however,  does  not  decussate.  To  recapitulate :  sensations  of  pain 
and  temperature  are  transmitted  through  the  lateral  columns,  and 
those  of  touch  and  weight  in  the  posterior  columns. 

What  is  the  path  of  the  motor  impulses  ? 

As  has  already  been  seen,  these  fibres  are  better  demonstrated 
than  the  sensory.  Most  of  the  motor  fibres  cross  to  the  opposite 
side  in  the  medulla  oblongata  (decussation  of  the  pyramids),  and 
the  impulses  pass  down  by  the  lateral  columns  in  the  crossed  or 
lateral  pyramidal  tract  on  the  side  opposite  to  that  in  which  they 
originate.  There  is  also  a  set  of  motor  fibres  which  do  not  cross, 
but  pass  directly  to  the  same  side  in  the  anterior  columns,  and 
decussate  in  the  anterior  or  white  commissure  near  the  point  of 
distribution.  The  destination  of  these  fibres  is  varif\ble,  for  the 
reason  that  the  amount  of  decussation  in  the  medulla  is  not  con- 
stant ;  but,  as  a  rule,  the  fibres  in  the  direct  tract  go  to  the  upper 
portion  of  the  body. 

Do  the  motor  tracts  carry  only  the  fiibres  arising  from  the  brain  ? 

No.  The  cells  in  the  anterior  cornu  of  the  gray  matter  of  the 
cord  originate  many  of  the  fibres  which  go  to  the  nerves.  This  is 
.demonstrated  after  division  of  the  cord  by  stimulating  these  fibres  : 
a  series  of  co-ordinated  motions  follows,  and  this  stimulus  may  be 
applied  direct  to  the  fibres  or  through  the  sensory  nerves. 

If  one  lateral  half  of  the  cord  be  cut  through  transversely,  what 
are  the  results? 

1.  Motor. — There  will  be  paralysis  of  motion  of  one-half  the  body 
below  the  section  ;  and  the  paralysis  will  be  of  the  same  side  if  the 
section  be  below  the  decussation  in  the  medulla ;  if  it  be  above,  the 
paralysis  will  cross  to  the  opposite  side. 

2.  Sensory. — Anaesthesia  of  the  opposite  side  below  the  section, 


SPINAL    CORD.  Ill 

and  the  loss  of  sensibility  will  be  complete.  At  the  same  time, 
on  the  same  sich:  as  the  section  the  sensory  function  may  be  ex- 
aiigorated,  and  there  may  be  /ii/penxsfhtsiu  to  such  a  degree  that 
even  a  touch  may  cause  exquisite  pain. 

What  results  follow  electrical  stimulation  of  the  posterior  columns 
of  the  cord  ? 
If  stimuli  be  applied  to  the  posterior  columns  of  the  cord  by 
a  galvanic  current,  signs  of  sensibility  are  shown  in  the  reflex 
actions ;  but  it  is  only  near  the  nerve-roots  that  the  sensibility 
seems  very  marked.  The  intensity  of  the  response  increases  with 
the  strength  of  the  current. 

What  reaction  follows  a  similar  stimulation  of  the  anterior  col- 
umns. 
Motion  in  the  parts  below,  and  the  motion  is  of  a  convulsive 
character.     No  pain  seems  to  accompany  the  convulsive  contrac- 
tions of  the  muscles. 

What  is  the  effect  in  the  lateral  columns? 

The  stimulation  of  the  anterior  portion  results  in  motion,  which 
gradually  decreases  as  one  approaches  the  posterior  nerve-roots, 
and  then  merges  into  the  signs  of  sensibility  similar  to  those 
excited  by  stimuli  applied  to  the  posterior  columns. 

What  practical  lesson  does  this  impress? 

That  inflammatory  changes  in  the  meninges  of  the  posterior 
portion  of  the  cord  excite  pain,  while  meningitis  of  the  anterior 
portion  excites  convuhsions. 

What  important  function,  besides  conduction,  does  the  spinal  cord 
perform  ? 
The  origination  of  motion  in  response  to  stimuli,  or  rej^ex  action. 

What  difficulties  present  themselves  in  the  study  of  the  reflex 
function  of  the  cord  in  mammals  ? 
The  great  shock  which  follows  injury  of  the  spinal  cord  in  mam- 
mals renders  the  study  of  its  function  difficult.  It  is  sometimes 
hours,  or  even  days,  before  any  experiments  can  be  conducted  after 
the  division  of  the  cord  in  a  warm-blooded  animal,  because  of  the 
failure  of  the"reflexes  to  act;  and  when  they  do  act  the  amount  of 
degeneration  which  has  followed  the  operation  is  uncertain.  Cold- 
blooded  animals   (especially   the  fi'og)  are  used  largely  iu  such 


112  NERVOUS   SYSTEM. 

experiments  for  this  reason,  and  it  is  probable  that  in  them  there 
is  a  greater  degree  of  this  kind  of  response,  though  of  the  same 
nature  as  in  mammals. 

How  are  the  reflex  actions  of  the  cord  classified? 

Into  cutaneous  and  muscular  reflexes. 

What  are  cutaneous  reflexes? 

Muscular  actions  which  follow  gentle  stimuli  applied  to  the  skin. 
The  plantar  reflex,  or  the  motion  'of  the  toes  and  foot  which  occurs 
on  tickling  the  sole  of  the  foot ;  the  cremaster  reflex,  or  retraction 
of  the  testicle  by  contraction  of  tne  cremaster  when  the  inner  side 
of  the  thigh  is  stimulated  ;  and  the  pupillary  reflexes,  contraction 
of  the  pupil  to  the  stimulus  of  light, — belong  to  this  class  of  cuta- 
neous reflexes. 

What  are  muscular  reflexes? 

Muscular  actions  which  follow  a  slight  blow  upon  a  muscle  or 
tendon  when  the  muscle  is  in  more  or  less  tension.  The  patellar 
reflex  is  a  well-known  example  of  this  form  of  action  :  if  the  knee 
be  flexed  to  a  right  angle  and  the  leg  allowed  to  hang  loosely,  the 
quadriceps  femoris  muscle  is  made  moderately  tense.  A  gentle 
tap  upon  the  tendon  of  the  muscle  below  the  patella  will  cause  the 
muscle  to  contract  and  the  leg  to  be  more  or  less  extended.  These 
reflexes  are  sometimes  called  tendon  reflexes. 

What  is  inhibition  of  reflex  action  ? 

The  ability  to  control  or  modify  reflex  action  by  an  efi"ort  of  the 
will  or  by  mental  action  which  is  not  consciously  voluntary.  As 
an  example  of  this,  if  the  palm  of  a  sleeping  child  be  touched  by 
the  finger,  the  baby's  hand  will  grasp  the  finger ;  but  if  the  child 
is  awake,  no  such  reflex  occurs,  but  is  checked  by  mental  action. 
Again :  one  may  avoid  crying  out  when  in  pain  by  an  effort  of  the 
will,  or  may  hold  the  feet  still  when  the  soles  are  tickled. 

Are  reflex  actions  frequent  in  the  ordinary  acts  of  life  ? 

They  are.  An  ordinary  act  which  has  become  habitual — for 
example,  walking — while  at  the  first  it  is  performed  as  a  voluntary 
muscular  act,  becomes  reflex  and  is  performed  without  conscious 
control  of  the  mind,  and  is  more  easily  and  more  gracefully  done 
when  no  attempt  is  made  to  direct  the  actions  of  the  muscles 
involved. 


TIIK    MEDriJ.A    OP.LONOATA.  113 

Do  the  reflexes  vary  in  strength  with  the  strength  of  the 
stimuli  ? 
A  stroni!;  stiimilus  will  excite  a  stronger  reflex  tluiii  a  mild  one. 
A  i)iii-i)riik  will  cause  the  foot  to  react  more  violently  than  tickling 
ihc  soil'.  In  certain  diseases  and  after  certain  pfiisons  these  actions 
licconK!  very  much  exaggerated:  tetanus  and  strychnine-poisoning 
])iit  the  corll  in  such  a  condition  that  a  very  slight  skin-irritation 
may  throw  the  entire  body  into  a  violent  convulsive  condition. 
Again,  other  diseases  or  drugs  decrease  the  irritability  of  the  cord. 

What  are  special  centres  for  reflex  action  ? 

Certain  actions  are  automatic — that  is,  may  take  phicc  without 
intervention  of  the  will  in  response  to  special  stimuli — and  these 
actions  are  dependent  upon  certain  nerve-centres  in  the  cord. 
These  centres  have  to  do,  noticeably,  with  sphincter  action  in  the 
pelvic  region,  and  the  centres  themselves  are  located  in  the  lumbar 
region  of  the  cord.  To  enumerate  some  of  the  automatic  actions 
of  these  centres  is  sufficient,  as  they  are  all  dependent  upon  special 
stimuli  and  special  centres  acting  upon  muscles  peculiar  to  the 
act.  They  are  defecation,  micturition,  emission  of  semen,  erection 
of  the  penis,  parturition.  There  are  numerous  other  automatic 
actions  besides  those  of  the  pelvic  sphincters,  but  the  mode  of 
operation  is  well  illustrated  by  these  functions. 

What  other  automatic  action  occurs  in  the  spinal  nerve-centres  ? 

Yaso-motor  centres  and  sweat-control  centres  are  in  the  cord, 
and  centres  which  control  the  nutrition  of  the  muscles,  as  well  as 
keep  them  tense  in  readiness  to  contract  effectively  ;  that  is,  main- 
tain the  tone  of  the  muscles.  The  nutrition  of  the  entire  body  is 
dependent  upon  the  maintenance  of  this  automatic  control  of  the 
vaso-motor  function,  as  is  shown  by  the  disorders  of  the  skin  and 
of  the  bones  and  joints  which  follow  spinal  injury  and  disease. 

What  influence  has  the  cord  upon  the  functions  controlled  by  the 
sympathetic  system? 
Very  great.      The  secretion  of  many  of  the  body  fluids  and  the 
control  of  the  organs  is  dependent  for  regulation  upon  the  connec- 
tion of  the  sympathetic  nerves  with  the  spinal  cord. 

THE   MEDULLA   OBLONGATA. 

Describe,  roughly,  the  medulla  oblongata. 

It  is  a  column  of  white  and  gray  nerve-substance,  and  is  an  en- 
8— Phy. 


114 


NERVOUS  SYSTEM. 


larged  portion  of  the  spinal  cord,  connecting  the  brain  with  the 
cord  below.  The  white  substance  is  composed  of  the  medullary 
fibres  connecting  brain  and  cord,  and  the  gray  matter  is  arranged 
variously  between  the  bands  of  white  fibres.  It  has  an  anterior 
and  a  posterior  fissure,  corresponding  to  those  of  the  lower  portion 
of  the  cord,  and  the  central  canal  of  the  cord  here  opens  into  the 
fourth   ventricle. 

How  do  the  columns  of  the  cord  arrange  themselves  in  the 
medulla  ? 

The  medulla  continues  in  a  general  way  the  arrangement  of  the 
fibres  in  tracts  of  the  cord  below,  but  as  the  diameter  is  greater  the 
general  shape  is  pyriform  and  the  shape  of  the  columns  nearly  pyra- 
midal  (Fig.  31).    The  anterior  columns  of  the  cord  become  the 

Fig.  31. 


Medulla  Oblongata  and  Pons  Varolii,  anterior  surface. 

anterior  pyramids  of  the  medulla ;  the  posterior  columns,  the  resti- 
form  bodies,  and  the  lateral  columns  correspond  to  the  lateral  tract 
of  the  medulla  with  the  olivary  bodies.  The  fibres,  however,  do 
not  follow  this  arrangement  so  closely,  but  the  columns  of  thfe  cord 
distribute  themselves  variously  in  the  medulla. 


THE  MEDULLA  OBLONGATA. 


115 


How  are  the  anterior  pyramids  made  up? 

TIk'  anterior  enluiiiiis  of  tlu'  cord  jscikI  their  fibres  (the  direct 
pyramidal  tract)  up  into  the  anterior  pyramids,  so  that  they  are 
continuous  tracts.  Other  fibres  from  the  lateral  columns  join  the 
fibres  of  the  anterior  pyramids,  and  here  cross  in  bundles  to  the 
opposite  side.  These  fibres  uiay  be  seen  crossing  the  anterior 
fissure  between  the  pyramids  by  gently  separating  the  auterior 
])yramids.  This  is  known  as  the  decusuition  of  the  pyrmnUIs.  The 
fibres  which  cross  in  this  way  belong  in  the  cord  to  the  portion  of 
the  lateral  column  known  as  the  crossed  or  lateral  pyramidal  tract. 

How  are  the  fibres  of  the  anterior  pyramids  distributed  to  the 
brain? 
Most  of  the  fibres  pass  on  through  the  pons  Varolii  to  be  dis- 
tributed in  the  cortex  of  the  brain.  Some  of  the  fibres  help  to 
make  up  the  fiJht,  and  pass  to  the  optic  thalamus,  while  others 
pass  to  the  cerebellum.  Fig.  32  shows  these  relations  very  sat- 
isfactorily. 

Fig.  32. 


OPTIC  .TnAUUtUl 


CeRCBCU.UM, 

Piagrani  of  the  Course  of  the  Fibres  throiich  the  ^Fedulla  to  the  Prain. 

How  does  the  lateral  column  of  the  cord  communicate  with  the 

brain  through  the  medulla? 

The  lateral  eoluniii  of  the  cord  is  broken  into  three  tracts  in  the 

medulla:  one,  we  have  just  seen,  joins  the  anterior  pyramid  of  the 

opposite  side  by  the  decussation  ;  a  second  joins  the  restiform  body 


116  NERVOUS  SYSTEM. 

on  its  way  to  distribution  in  the  cerebellum  ;  wliile  the  third  set  of 
fibres  goes  to  the  fasciculus  teres,  and  reaches  the  ganglia  at  the 
base  of  the  brain.     (See  Fig.  32.) 

What  is  the  mode  of  connection  of  the  posterior  column  of  the 
cord? 

Its  fibres  continue  on  as  the  posterior  pyramid  of  the  medulla 
and  restiform  body.  The  former  probably  communicates  with  the 
basal  ganglia,  though  it  has  not  been  traced  as  far,  and  the  latter 
(restiform  body)  for  the  most  part  reaches  the  cerebellum.* 

What  are  the  olivary  bodies? 

Each  is  a  mass  of  white  nerve-substance  containing  a  central 
gray  nucleus.  There  are  communications  between  it  and  some  of 
the  tracts  from  the  cord,  especially  from  those  tracts  of  the  ante- 
rior and  lateral  columns  which  go  to  the  ganglia  at  the  base  of  the 
brain. 

How  is  the  gray  substance  arranged  in  the  medulla  oblongata  ? 

As  the  fibres  which  form  the  crossed  pyramidal  tract  pass  from 
the  lateral  tract  to  decussate  into  the  anterior  pyramid  of  the 
opposite  side,  they  push  the  anterior  cornu  of  the  gray  matter 
backward ;  and  this  is  still  further  accomplished  by  the  olivary 
body,  until  the  gray  matter  is  spread  out  upon  the  posterior  sur- 
face of  the  medulla  at  its  upper  part.  Here  the  central  canal  of 
the  cord  has  widened  out  to  form  the  fourth  ventricle,  and  the 
gray  substance  is  aggregated  to  form  the  floor  of  the  ventricle. 
There  are  some  other  collections  of  gray  matter — for  example,  in 
the  olivary  bodies — but  this  is  the  principal  accumulation. 

What  especial  importance  has  this  collection  of  gray  substance  in 
the  floor  of  the  fourth  ventricle  ? 

In  this  nucleus  are  the  origins  of  some  of  the  cranial  nerves : 
the  spinal  accessory,  hypoglossal,  pneumogastric,  and  glosso-pharyn- 
geal  nerves,  and  a  root  of  the  auditory  of  the  facial,  and  of  the 
trigeminus  nerves,  arise  in  this  important  collection  of  gray  matter. 

*  In  speaking  of  these  fibres  it  has  been  convenient  to  say  that  they 
"  pass "  in  certain  directions  or  "  are  distributed "  in  some  situation.  It 
must  not  be  forgotten  that  they  are  afferent  and  efferent  medullated  nerve- 
fibres,  and  that  such  terms  must  be  considered  as  somewhat  figurative.  In 
reality,  it  would  not  seem  proper  to  speak  of  an  efferent  fibre  as  being  "  dis- 
tributed "  at  its  origin,  but  convenience  and  usage  permit  the  use  of  these 
and  similar  expressions. 


THE  MEDULLA  OBLONGATA.  117 

Of  the  sinaller  t'ollection.s  ui"  gray  substance,  probably  none  has  the 
pot'uliar  interest  which  the  floor  of  the  fourth  ventricle  possesses 
for  tliis  reason. 

What  are  the  functions  of  the  medulla  oblongata  ? 

The  luotlulhi  has  practically  the  same  I'unctiuns  as  the  cord, 
conduction  and  reflexion  ;  but  in  both  these  qualities  it  excels  the 
cord,  for  in  the  conduction  of  impulses  it  has  to  transmit  all  that 
pass  between  the  brain  and  spinal  system,  and  in  the  reflex  actions 
which  it  oriiiinates  it  is  much  more  elaborate  than  the  cord.  The 
automatic  reflex  actions  of  the  medulla  involve  the  rhythm  of  the 
vital  organs,  respiration  and  heart-action. 

How  may  the  functions  of  the  medulla  be  demonstrated  in  the 
frog  ? 

If  the  spinal  cord  be  removed  up  to  the  medulla,  the  respirations 
continue,  and  in  the  same  way  they  do  not  cease  if  the  brain  be 
removed  without  disturbing  this  organ,  or.  if  both  cord  and  brain 
be  removed  without  disturbing  the  medulla,  the  movements  of 
breathing  will  continue.  If  the  medulla  is  injured  at  the  origin 
of  the  pneumogastric  nerve,  however,  the  movements  of  respiration 
cease  and  the  animal  dies.  The  same  occurs  when  a  similar  injury 
occurs  in  the  higher  animals  and  in  man.  Death  occurs  instanta- 
neously in  this  way  when  the  medulla  is  broken  near  the  axis  in 
executions  by  hanging — "  the  neck  is  broken  " — or  an  animal  is 
killed  by  "  pithing "  in  laboratory  experiments. 

What  are  the  special  centres  in  the  medulla  ? 

There  are  a  considerable  number  of  centres  in  the  medulla 
which  control  many  important  and  complicated  co-oi'dinatcd  mus- 
cular actions.  These  are  centres  of  reflex  action  for  the  most  part  ; 
that  is,  ai'e  called  upon  to  act  in  response  to  stimuli  derived  from 
an  aflTeront  impulse  or  to  a  voluntary  effort. 

What  is  meant  by  automatism  of  the  medulla? 

The  impulses  wliicli  are  sent  out  to  muscles  without  apparent  afl^er- 
ent  stimuli,  and  without  an  eftort  of  the  will,  are  called  automatic. 
Such  rhythmic  impulses  as  those  which  maintain  the  respiratory 
function  belong  to  this  class.  It  is  not  to  be  doubted  that  such 
actions  are  reflex  and  in  response  to  stimuli.  In  the  case  of  the 
lungs,  for  example,  the  presence  of  deoxygcnated  blood  may  serve 
to  excite  an  afferent  impulse.     Nevertheless,  .some  authors  distin- 


118  NERVOUS  SYSTEM. 

guish  between  automatism  and  reflex  action.  This  automatic  action 
cannot  be  considered  as  at  all  the  same  as  an  action  of  the  brain 
proper,  like  volition,  but  rather  as  a  high  grade  of  reflex  action. 

What  other  functions  are  attributed  to  the  medullary  centres? 

The  control  or  inhibition  of  action  through  the  nerves  which  are 
distributed  from  this  region  and  through  the  communications  with 
other  centres  in  the  cord.  Further  than  this,  there  are  supposed 
to  lie  in  the  medulla  centres  which  maintain  the  nutrition  and  tone 
of  the  muscles.     These  are  known  as  control  and  tonic  centres. 

Name  some  of  the  reflex  functions  depending  upon  the  centres  in 
the  medulla. 

(1)  The  portion  of  digestion  which  is  performed  in  the  mouth  is 
dependent  upon  medullary  reflexes — mastication,  deglutition,  and 
the  secretion  of  saliva,  and,  probably,  of  the  pancreatic  and  other 
digestive  juices.  In  this  connection  the  so-called  vomiting  centre 
may  be  noted. 

(2)  The  resph-atory_  functions  are  so-called  automatic  functions 
of  the  medulla,  and  are  capable  of  being  sustained  by  the  nerve- 
force  derived  from  the  medulla  alone.  The  centres  for  cotigliing 
and  sneezing  are  also  here.  The  pneumogastrie  and  phrenic  nerves 
convey  the  afferent  and  eff"erent  stimuli,  though  there  may  be 
communications  with  other  nerves  whereby  sensory  stimuli  are 
applied. 

(3)  Regulation  of  the  heart's  action  is  found  here,  both  inhihitory 
and  accelerator  centres  communicating  through  the  vagus. 

(4)  Vaso-motor, — regulation  of  the  unstriped  muscular  fibre 
of  the  arteries  is  also  accomplished  by  the  medulla.  A  peculiar 
vaso-motor  disturbance  is  brought  about  by  injur}'^  of  one  centre  of 
the  medulla — namely,  the  interference  with  the  glyeogen-function 
of  the  liver  and  the  appearance  of  sugar  in  the  urine — the  diabetic 
centre. 

(5)  Various  centres  which  have  to  do  with  the  regulation  of  the 
hody-temperature.  The  vaso-motor  centres  we  have  already  men- 
tioned. There  are  also  found  special  sj^ea^centres ;  and,  further- 
more, a  control  of  the  special  sweat-centres  found  in  the  cord  is 
here  maintained.  Upon  plausible  theoretical  grounds  there  is  also 
assumed  to  be  a  heat-inliihitory  centre,  by  which  the  heat-produc- 
tion is  controlled  without  reference  to  vaso-motor  conditions. 


THE   PONS   VAROLII   AND  CRURA   CEREBRI.  119 

What  other  important  functions  are  supposed  to  belong  to  the 
gray  matter  of  the  medulla  ? 
The  ()ri<z;iii  of  tlic  roots  of  certain  of  the  cranial  nerves  here  lias 
caused  the  special  senses  of  he.nrlnij  and  of  ((t^^tc,  to  be  referred  to  this 
region  ;  and  the  connection  with  the  sympathetic  system  through  the 
cord  has  caused  the  centre  for  the  dilatation  of  the  j)^i}>il>  to  be  located 
in  the  medulla.  Plionation  is  also  dependejit  upon  the  action  of 
nerves  arising  in  this  focus  of  gray  matter,  and  no  voluntary  or 
reflex  sound  can  be  produced  by  an  animal  in  which  the  speech- 
centre  in  the  uiedulla  is  destroyed.  The  origin  here  of  the  hypo- 
glossal and  pneumogastric  nerves,  involving  as  they  do  the  move- 
ments of  the  tongue  and  glottis,  controls  both  the  acts  of  plionation 
and  articulation. 

What  is  glosso-labio-laryngeal  paralysis? 

It  is  a  progressive  degeneration  of  the  gray  matter  of  the  me- 
dulla, and  it  shows  itself  first  in  a  paralysis  of  the  tongue,  which 
renders  articulation  of  certain  sounds  indistinct :  as  the  degenei'a- 
tion  progresses  in  the  medulla  the  articulation  becomes  more  and 
more  impossible  and  deglutition  is  affected.  The  disease  continues 
to  aff'ect  more  and  more  of  the  functions  dependent  upon  the  me- 
dulla, until  death  ensues  as  a  result  of  involvement  of  the  cardiac 
and  respiratory  centres  or  of  inability  to  take  food.  It  is  some- 
times called  bulbar  paralysis. 

With  such  varied  and   important  powers,  can  the  medulla  be 
classed  as  an  organ  of  the  mind  ? 

It  cannot,  for  the  reason  that  it  has  no  voluntai'y  control  of  any 
of  its  poAvers.  They  are  all  reflex,  or  respond  to  volition  originat- 
ing elsewhere  in  the  brain.  Though  the  regulation  of  the  action 
of  the  heart  and  of  the  lungs  is  dependent  upon  the  medulla,  and 
many  other  functions  of  absolute  need  nuiy  be  given  to  it,  yet  its 
power  is  not  of  a  character  to  permit  it  to  be  called  an  organ  of 
the  mind. 

THE   PONS   VAROLII   AND   CRURA   CEREBRI. 
What  is  the  pons  Varolii  ? 

It  is  a  collection  of  nervous  tissue  lying  innnediately  above  the 
medulla.  It  consists  of  white  fibres,  with  areas  of  gray  matter 
filling  in  the  intervals  between  the  fasciculi  of  white  fibres.  The 
white  fibres  connect  the   brain   with  the  medulla,  and  join   the 


120  NEEVOUS   SYSTEM. 

various  parts  of  the  brain  one  to  another.  What  is  the  function 
of  the  gray  matter  is  little  known,  but  it  is  directly  continuous 
with  that  of  the  medulla,  and  probably,  like  it,  active  as  a  centre 
of  nervous  force.  The  median  line  of  the  pons  is  marked  by  the 
decussation  of  many  nerve-fibres,  and  it  is  probable  that  the  fibres 
of  the  facial  nerve  arising  in  the  floor  of  the  fourth  ventricle  decus- 
sate here. 

What  peculiar  paralyses  are  caused  by  lesions  of  the  pons  ? 

The  so-called  crossed  paralysis  may  follow  lesions  in  the  lower 
portion  of  the  pons  ;  that  is,  paralysis  of  sensation  and  motion, 
more  or  less  complete,  of  the  opposite  side  of  the  body,  with  paraly- 
sis of  the  facial  muscles  of  the  same  side  as  the  lesion. 

Describe  the  crura  cerebri. 

The  crura  are  formed  largely  of  fibres  passing  from  the  medulla, 
through  the  pons  Varolii,  to  the  hemispheres  of  the  cerebrum.  They 
divide  so  as  to  form  two  sets  of  fibres  :  the  more  superficial  (crusta) 
are  mostly  motor  or  eiferent  fibres  which  are  continuous  with  the 
pyramidal  tracts  in  the  cord ;  while  the  deeper  (tegmentum)  layer 
of  fibres  are  afferent  or  sensory,  and  are  derived  largely  from  the 
lateral  and  posterior  tracts  of  the  cord.  Lying  between  these 
bands  of  fibres  is  a  mass  of  gray  substance  (locus  niger)  whose 
function  as  a  nerve-centre  is  not  understood,  though  it  has  to  do 
with  co-ordination  of  the  muscles,  and  especially  with  regulation 
of  the  muscles  controlled  by  the  motor  oculi  nerve. 

What  paralyses  follow  lesions  in  the  crura  cerebri? 

Paralysis  of  the  opposite  side  of  the  body,  both  of  sensation  and 
motion,  and  of  a  degree  of  intensity  depending  upon  the  size  of  the 
lesion,  and,  besides  this,  paralysis  of  the  motor  oculi  nerve  of  the 
same  side  as  the  lesion.  There  is  a  derangement  of  the  ordination 
of  motions  which  follows  lesions  of  this  region  beyond  that  which 
belongs  to  the  motor  paralysis  ;  this  is  often  shown  in  rotary  move- 
ments when  the  subject  attempts  to  walk.  It  is  inferred  that  there 
are  co-ordinating  influences  derived  from  the  crura. 

What  is  the  function  of  the  corpora  quadrigemina  ? 

The  corpora  quadrigemina  are  the  homologues  of  the  optic  lobes 
in  some  of  the  lower  animals,  and  may  be  regarded  as  important 
centres  for  the  visual  and  motor  functions  of  the  eyes.  Not  only 
does  blindness  follow  lesions  of  the  corpora  quadrigemina,  but 
there   is   often  atrophy  of  them   when   the   eyes   are  destroyed. 


THE    CEREBUUM.  121 

Their  action  is  crossed  ;  that  is,  lesions  of  tlic  left  side  priiducc 
right  blindness.  From  these  bodies  also  is  derived  the  power  of 
co-ordination  of  the  movements  of  the  eyes  and  the  control  of  the 
the  reflex  of  the  pupil.  These  centres  arc  closely  related,  and 
the  disturbance  of  the  one  by  a  lesion  in  this  part  usually  involves 
the  other. 

THE   CEREBRUM. 
Describe  briefly  the  cerebrum. 

It  is  composed  of  two  parts,  or  /leiiiisjilicrcti,  connected  by  a  com- 
missure of  white  fibres,  the  corjms  cal/osmn.  The  two  hemispheres 
are  separated  by  a  deep  fissure  extending  fore  and  aft,  and  in  the 
interior  of  each  is  found  a  cavity  known  as  the  lateral  ventricle. 
The  hemispheres  are  connected  directly  with  the  spinal  system  by 
the  crura  cerebri  and  medulla,  and  with  each  other  b}'  the  corpus 
callosum.  They  are  composed  of  white  and  gray  nerve-substance, 
and  the  latter  is  arranged  largely  at  the  periphery  of  the  hemi- 
spheres;  the  former  being  made  up  of  communicating  nerve-fibres 
which  connect  the  various  portions  of  the  hemispheres,  and  the 
hemispheres  with  other  parts  of  the  cerehro-spinal  system,  thus 
allowing  a  free  control  of  the  impulses  arising  from  one  cell  or  set 
of  cells  by  other  cells  in  the  gray  matter. 

How  is  the  surface  of  the  cerebrum  marked  ? 

It  is  divided  into  regions  bv'  Jissiircs.  -which  separate  one  part 
from  another.  These  fissures  are  always  present,  and  upon  them 
depends  the  determination  of  the  division  of  the  cerebrum  into 
lobes.  The  fissures  which  are  of  most  use  in  locating  the  lobes  of 
cerebral  matter  are  the  fissure  of  Kolando,  the  fissure  of  Sylvius, 
and  the  parieto-occipital  fissure. 

What  are  the  convolutions  of  the  cerebrum  ? 

The  surface  of  the  brain  is  further  cut  up  by  a  number  of  other 
clefts,  known  as  sulci ;  and  these  separate  the  surface  into  a  num- 
ber of  distinct  masses  or  convolutions.  The  depth  of  the  sulci 
and  their  number  determine  the  quality  of  the  brain  in  respect  to 
its  degree  of  development ;  thus,  the  convolutions  in  man  are  much 
deeper  and  more  numerous  than  in  the  lower  animals.  The  sulci 
are  not  invariable  in  position  or  number  in  different  brains. 

Into  what  regions  is  the  cerebrum  divided  by  the  fissures  ? 

(1)  Fro)itul  L(j})e. — This  lube  is  bounded  by  the  fissure  of  Kolando, 


122 


NEEVOUS  SYSTEM. 


and  contains  several  convolutions  which  include  the  forward  por- 
tion of  the  brain. 

(2)  The  Parietal  Lobe  lies  behind  the  fissure  of  Rolando,  and 
extends  posteriorly  to  the  occipito-parietal  fissure.  The  convolu- 
tions are  well  marked,  and  are  separated  by  a  well-marked  sulcus 

Fig.  33. 


Plan  of  the  Human  Brain  in  Profile,  showing  its  fissures  and  convolutions :  S,  fissure  of 
Sylvius ;  S',  anterior  branch;  S",  posterior  branch  ;  R,  fissure  of  Rolando  ;  P,  parieto- 
occipital fissure. 

(sometimes  known  as  the  parietal  fissure),  and  the  posterior  branch 
of  the  fissure  of  Sylvius  is  often  enfolded  by  the  inferior  parietal 
convolution.  (In  Fig.  33  this  convolution  is  marked  "  Supramar- 
ginal  convolution.") 

(3)  The  Temporo-sphenoidal  Lobe  is  below  the  Sylvian  fissure 
and  in  front  of  the  parieto-occipital.  Its  convolutions  are  well 
marked. 

(4)  The  Occipital  Lobe  is  found  at  the  posterior  end  of  the  cere- 
bral hemisphere,  and  its  convolutions  are  continuous  with  those  of 
the  parietal  and  temporo-sphenoidal  lobes,  except  within  the  longi- 
tudinal fissure,  where  it  is  cut  ofi'  from  them  by  the  parieto-occipital 
fissure. 


THE   CEREBRUM. 


123 


Hori/ontal  Section  of  the  IIeuiisi>lieres  at  the  Level  of  the  Cerebral  Ganglia :  1,  great 
longitudinal  fissure  between  frontal  lobes;  2,  great  longitudinal  fissure  between 
occipital  lobes  ;  H,  anterior  part  of  curpus  callosum  ;  4,  fissure  of  Sylvius  ;  fi,  convolu- 
tions of  the  insula;  (!,  caudate  nucleus  of  corpus  striatum;  7,  lenticular  nucleus  of 
corpus  striatum;  8,  optic  thalamus;  9,  internal  capsule;  10,  external  capsule;  11, 
claustrum. 

(5)  The  Central  Lohc.  or  hland  of  Rcil.  is  within  the  fissure  of 
Sylvius  and  covered  by  the  convolutions  of  the  frontal  and  parietal 
lobes.     (See  5  in  Fig.  84.) 

Besides  these  well-defined  lobes,  the  portion  of  the  cerebral  sur- 


124 


NEEVOUS  SYSTEM. 


face  which  is  within  the  longitu- 
dinal fissure  is  marked  by  sulci 
and  conA'^olutions.  The  convolu- 
tions of  the  frontal,  parietal,  and 
occipital  lobes  are  found  here, 
and  the  marginal  (or  calloso- 
marginal)  convolution,  lying 
above  the  corpus  callosum,  is 
the  principal   landmark. 

How  is  the  gray  matter  of  the 
cerebrum  arranged? 

The  increase  in  the  area  of 
the  surface  of  the  hemispheres 
by  the  infolding  of  the  sulci 
adds  very  greatly  to  the  amount 
of  gray  substance  in  the  brain  ; 
for  the  entire  surface  is  com- 
posed of  gi'ay  substance,  and  this 
follows  the  sulci  and  fissures 
(Fig.  34)  in  all  their  folds,  and 
is  not  cut  into  by  them.  Be- 
sides the  gray  matter  in  the  con- 
volutions there  are  certain  other 
gray  masses  in  the  substance  of 
the  white  matter :  the  optic 
thalami,  the  corpora  striata,  and 
the  claustrum  (Fig.  34)  are  the 
chief  of  these  gray  masses. 

What  is  the  minute  structure 

of  the  gray  matter  of  the 

cortex  ? 

The  gray  matter  of  the  cortex 

is  made  up  of  ganglion-cells  of 

various  shapes  and  sizes  lying  in 

a  loose  connective-tissue  stroma. 

The   connective   tissue    is    more 

abundant  at  the   surface.     The 

cells  are  the  source  of  numerous 

nerve-fibres  which  pass  out  into 

the  white  matter  (Fig.  35).  There 

are  counted  five  layers  of  these 


Gray  Matter  of  the  Cerebral  Cortex  (Meynert).  ganglionic     tisSUes,     and,     while 


THE  CEREBRUM.  ,  125 

these  zones  merge  into  one  anotlier,  tliey  are  tDlerably  distiiiet.  In 
the  niichlle  (and  widest)  layer  hirge  niultijxdar  cells  are  very  nume- 
rous, and  the  fibres  may  be  seen  to  ])ass  throiiiili  the  deej)er  layers 
in  bundles  into  the  white  matter. 

What  chemical  peculiarities  does  nervous  tissue  present? 

It  contains  some  peculiar  bodies  allied  to  the  fats,  but  contain- 
ing nitrogen  :  of  these  cerehrin  and  kcethin  are  the  more  prominent. 
Aside  from  this,  the  constituents  are  proteid  and  fatty  substances, 
with  salts,  chiefly  potassium  and  magnesium  phosphates,  and 
water. 

What  is  the  weight  of  the  adult  brain  ? 

About  3  pounds.  In  size  it  exceeds  the  brains  of  all  the  lower 
animals  except  the  elephant  and  whale.  Its  weight  is  about  one- 
fortieth  of  the  total  body-weight,  and  this  ratio  is  greater  than  in 
the  lower  animals,  with  a  few  exceptions  among  the  smaller  birds 
and  monkeys.  In  women  the  weight  is  about  one-tenth  less  than 
in  men. 

Is  the  size  of  the  brain  a  criterion  of  intellect  ? 

In  some  degree  it  is,  but  this  is  not  absolute.  The  depth  of  the 
sulci,  and  consequent  size  and  complexity  of  the  convolutions,  are 
a  more  efficient  measui-e  of  the  brain-power.  In  the  largest  of  the 
apes  the  brain  of  an  adult  animal  is  about  the  same  in  weight  as 
that  of  a  human  infant  at  birth.  Idiots,  as  a  rule,  have  brains 
much  smaller  than  the  normal,  and  in  them  the  convolutions  are 
apt  to  be  ill-marked  and  uncomplicated,  as  is  the  case  in  the  lower 
animals. 

What  is  known  of  the  course  of  the  fibres  in  the  white  substance 
of  the  hemispheres  ? 

The  course  of  these  fibres  may  be  classified  in  three  groups  : 
1,  commissural  fibres;  2,  fibres  of  association;  and  3,  medullary 
fibres. 

(1)  The  Commissural  Fibres  are  those  which  connect  one  hemi- 
sphere with  the  other,  and  it  may  be  said  that  these  fibres  connect 
each  set  of  convolutions  with  the  corresponding  set  of  the  opposite 
side.  The  convolutions  of  the  portion  of  the  brain  lying  above  the 
fissure  of  Sylvius  communicate  by  the  corpus  callosum,  while  those 
at  the  base  of  the  brain  are  joined  by  fibres  passing  through  the 
anterior  commissure. 


126  NERVOUS   SYSTEM. 

(2)  Fibres  of  Association  are  those  fibres  which  connect  the 
convolutions  of  one  hemisphere.  These  fibres  pass  in  bundles  just 
beneath  the  cortical  gray  matter  of  the  convolutions,  and  it  is 
thought  that  most  of  the  important  convolutions  of  each  hemi- 
sphere intercommunicate  in  this  way. 

(3)  The  Medullary  Fibres  are  those  which  connect  the  cerebrum 
and  medulla,  and  are  regarded  as  indirect  and  direct,  according  as 
they  do  or  do  not  pass  to  the  gray  ganglia  at  the  base  of  the  brain. 
In  considering  the  course  of  the  fibres  from  the  medulla  through 
the  crura  cerebri  it  was  noted  that  the  motor  and  sensory  fibres 
were  to  some  extent  separated.  The  fibres  pass  from  the  crura  to 
the  internal  capsule,  and  here  the  course  of  the  fibres  is  twofold : 
the  "  direct  fibres "  pass  to  the  cerebral  convolutions  through  the 
corona  radiata,  while  the  "indirect  fibres"  pass  to  the  corpora 
striata,  and  optic  thalami,  and  communicate  with  ganglion-cells 
there. 

What  is  the  function  of  the  corpora  striata  and  the  optic  thalami  ? 

These  "  basal  ganglia,"  with  the  other  collections  of  gray  sub- 
stance outside  the  convolutions,  seem  to  have  a  controlling  influ- 
ence upon  the  spinal  system.  The  crura  throw  their  fibres  largely 
to  these  ganglia,  the  motor  pyramidal  tracts  to  the  corpora  striata, 
and  the  sensory  fibres  from  the  lateral  and  posterior  tracts  to  the 
optic  thalami.  It  is  through  these  ganglia  that  all  voluntary 
impulses,  except  those  by  the  direct  medullary  fibres,  must  pass. 
These  basal  ganglia  communicate  through  the  corona  radiata  with 
the  convolutions  of  the  cortex,  and  it  is  probable  that  we  may 
regard  this  part  as  acting  as  a  middleman  to  elaborate  and  co- 
ordinate the  voluntary  impulses  of  the  cortex  and  to  act  in  the 
matters  not  requiring  the  intervention  of  the  higher  endowments 
of  the  mind.  This  status  of  these  ganglia  is  quite  theoretical,  but 
the  function  may  be  considered  as  a  sort  having  the  properties  of 
both  the  automatism  of  the  gray  matter  of  the  medulla  and  cord 
and  the  voluntary  function  of  convolutions.  In  this  consideration, 
however,  we  must  not  undervalue  the  communication  with  the 
cortex  which  these  basic  ganglia  possess. 

Do  lesions  in  these  basic  ganglia  cause  peripheral  symptoms? 

No.  So  far  as  has  been  observed,  the  corpora  striata  may  be 
involved  by  considerable  lesions  without  causing  persistent  motor 
or  sensory  disturbances,  and  the  same  may  be  said  of  the  optic 


THE  CEREBRUM.  127 

thalanii,  but  if  the  lesion  eneroaclies  upon  the  white  matter  of 
the  internal  capsule  or  crura  cerebri,  the  effect  is  to  cause  more 
or  less  paralysis,  depending  upon  the  severity  of  the  lesion  and 
its  position. 

What  are  the  functions  of  the  cerebrum  ? 

The  motor  and  sensory  functions  which  have  been  seen  to  belong 
to  other  nuclei  of  gray  matter  are  centred  here,  but  infinitely 
broadened,  for  the  cells  in  the  convolutions  of  the  cerebrum  can 
originate  the  efferent  and  perceive  the  afferent  nerve-impulses. 
In  fact,  it  is  in  this  portion  of  the  brain  that  the  intelligence  is 
centred:  it  is  the  organ  of  the  mind.  Memory,  reason,  emotions, 
and  all  the  other  attributes  of  the  mind  are  dependent  upon  its 
functional  power. 

What  is  the  effect  upon  animals  of  the  removal  of  the  hemi- 
spheres ? 

In  some  of  the  lower  animals  the  cerebrum  may  be  entirely 
removed  without  killing  them.  When  this  is  done,  for  example, 
in  the  case  of  a  pigeon,  the  bird  remains  quiet  in  one  position,  and 
is  not  disturbed  by  noises,  or  if  thrown  from  its  perch  it  flies  and 
alights  in  a  nearly  normal  manner.  If  a  foot  be  pinched,  it  with- 
draws it  and  perhaps  changes  its  position.  The  bird  is  capable 
of  reflex  actions  of  various  complicated  kinds,  but  there  is  no 
spontaneous  exercise  of  volition  :  all  its  movements  are  excited 
by  the  nerve-stimuli  of  the  moment.  There  is  no  perception  of 
stimuli ;  the  intelligence  is  gone. 

What  is  unilateral  action  of  the  brain  ? 

There  are  instances  in  which  the  injury  or  disease  of  one-half  of 
the  brain  has  left  the  intellectual  faculties  not  gravely  impaired. 
From  a  consideration  of  such  cases  it  has  been  held  that  the  action 
of  one  of  the  hemispheres  was  sufficient  for  the  purposes  of  the 
mind.  There  is,  however,  an  absolute  dependence  for  motor  and 
sensory  functions  upon  the  integrity  of  both  sides,  for  the  one  side 
cannot  act  for  the  other  in  these  functions.  As  a  rule,  it  is  safe 
to  assume  that  the  two  hemispheres  act  in  unison. 

Are  the  functions  of  the  brain  localized  ? 

While  the  brain  is  regarded  as  an  nrgan  of  the  mind,  it  is  prob- 
able that  the  various  functions  may  be  regarded  as  belonging  to 
definite  portions  of  the  convolutions  which  are  appropriated  for  that 


128  NERVOUS   SYSTEM. 

purpose.  The  functions  of  the  convolutions  have  not  been  assigned, 
except  for  a  very  small  portion  of  the  brain-surface  and  for  some 
of  the  simpler  actions.  For  the  most  part,  our  knowledge  of  the 
localization  of  brain-functions  is  confined  to  "motor  areas,"  in  which 
it  has  been  determined  that  stimulation  of  a  certain  group  of  cells 
will  cause  a  definite  action.  Besides  this,  certain  other  centres  are 
located,  as  of  sight  and  speech. 

How  are  the  motor  areas  determined? 

When  the  surface  of  the  brain  is  exposed  in  animals  or  in  man, 
the  stimulation  of  certain  areas  of  the  cortex  by  a  mild  electrical 
current  will  give  rise  to  motion  in  the  peripheral  muscles  ;  and  it  is 
found  that  the  stimulation  of  the  same  region  in  the  same  or  other 
animals  will  cause  the  same  results.  These  centres  of  motor  im- 
pulses are  situated  almost  entirely  upon  the  convolutions  about  the 
fissure  of  Rolando  (Fig.  36). 

What  is  known  regarding  the  localization  of  sensory  areas  ? 

This  has  not  been,  by  any  means,  so  definitely  fixed  as  for  motor 
centres ;  but  the  centres  for  sensation  may  be  said  to  exist,  and 
probably  in  the  convolutions  of  the  posterior  portion  of  the  cere- 
brum. The  centre  for  vision  in  the  convolutions  about  the  poste- 
rior branch  of  the  fissure  of  Sylvius  is  generally  accepted  (14,  15, 
in  Fig.  36).  The  centre  for  hearing  is  tolerably  defined  in  the 
temporo-sphenoidal  lobe  along  the  posterior  branch  of  this  fissure 
(16,  Fig.  36).  The  speech-centre  is  also  located  with  seeming  ac- 
curacy along  the  anterior  branch  of  the  fissure  of  Sylvius  and  in  the 
island  of  Reil.  This  centre  seems  to  be  much  more  developed  upon 
the  left  side  of  the  brain.  In  Fig.  36  this  centre  may  be  indicated 
roughly  by  reference  to  the  tongue-centres  (8  and  9). 

Do  the  evidences  of  pathology  agree  with  these  experiments  ? 

Injuries  and  diseases  involving  the  motor  areas  are  followed  by 
paralysis  so  well  defined  that  it  is  frequently  possible  to  locate 
the  seat  of  the  lesion  from  its  result  upon  the  inuscular  system. 
Tumors,  abscesses,  and  depressed  bone,  for  example,  are  capable 
of  accurate  localization  in  this  way.  The  more  indefinite  sen- 
sory paralyses  do  not  so  accurately  point  out  their  origin.  On 
the  whole,  the  evidence  of  pathology  bears  out  in  full  the  experi- 
mental results.  The  crossed  action  of  all  the  nervous  structures 
is  especially  to  be  noted.      In  the  case  of  a  right  paralysis  in 


THE  CEREBRUM. 


129 


which  the  speech  is  affected,  as  compared  with  a  left  heniiple<ria 
and  speech  unaffected,  this  crossed   action   is   impressed  when   we 


Fio.  36. 


Brain  of  Monkey,  showing  the  position  of  the  motor  and  sensory  centres  as  ascertained 
by  Ferrier.  The  actions  all  occur  on  the  side  of  the  body  opposite  to  the  part  of  the 
brain  irritated  :  1,  the  eyes  open  widely,  the  pupils  dilate',  and  bead  and  eyes  turn  to- 
ward opposite  side  ;  2,  extension  forward  of  the  opposite  arm  and  hand,  as  if  to  reach 
something  in  front ;  3,  movements  of  tail  (and  trunk) ;  4,  retraction  with  adduction  of 
opposite  arm  ;  5,  supination  and  Ilex  ion  of  the  forearm,  by  which  the  arm  is  raised  to- 
ward the  mouth  ;  fi,  action  of  zygonKities,  by  which  the  angle  of  mouth  is  retracted  and 
elevated;  7,  elevation  of  alaof  nose  and  upper  lip;  8,  opening  of  mouth  with  protnision 
of  tongue;  9,  retraction  of  tongue;  10,  retraction  of  opposite  angle  of  mouth  ;  a,b,c,(l, 
prehensile  movements;  11,  retraction  and  adduction  of  opposite  arm  ;  12,  advance  of 
the  opposite  hind  limb;  13,  complex  movements  of  thigh,  leg,  and  foot;  14, 15,  vision 
(sensory) ;  16,  hearing  (sensory). 

remember  the   localization   of  the    centre  for  speech  in  the  left 
hemisphere  near  the  motor  area. 

Mention  some  of  the  common  terms  used  in  defining  paralysis. 

Anaesthesia  =  loss  of  sensation. 

Hemianaesthesia  =  loss  of  sensation  in  one  lateral  half  of  the 
body. 

Hemiplegia  =  loss  of  muscular  power  in  one  lateral  half  of  the 
body. 

Paraplegia  =  symmetrical  loss  of  muscular  power  in  the  lower 
portion  of  the  body  and  extremities. 

9— Phy. 


130  NERVOUS  SYSTEM. 

Aphasia  =  loss  of  power  to  talk — amnesic  when  words  are  for- 
gotten ;  ataxic  when  the  power  to  articulate  is  lost,  though  the 
words  are  known. 

THE  CEREBELLUM. 
Describe  the  cerebellum. 

It  is  a  mass  of  nerve-substance  situated  posteriorly  at  the  base 
of  the  skull.  It  consists  of  a  median  lobe  and  two  lateral  hemi- 
spheres, and  is  connected  with  the  rest  of  the  cerebro-spinal  system 
by  numerous  white  fibres  collected  in  bundles  known  as  peduncles. 
Of  these,  the  larger  peduncles  pass  to  and  largely  make  up  the  pons 
Varolii  (middle  peduncles),  thus  connecting  the  lateral  hemispheres 
of  the  cerebellum.  The  superior  peduncles  (or  processus  e  cerebello 
ad  testes)  pass  beneath  the  corpora  quadrigemina,  and  the  fibres  pass 
into  the  white  matter  of  the  cerebrum,  decussating  as  they  meet 
beneath  the  corpora  quadrigemina.  The  inferior  peduncles  pass  to 
the  medulla,  where  they  form  the  restiform  bodies.  Thus  it  is  seen 
that  the  entire  cerebro-spinal  system  communicates  very  freely  with 
the  cerebellum. 

How  is  the  gray  matter  of  the  cerebellum  arranged  ? 

The  arrangement  in  convolutions  is  not  the  same  as  in  the  cere- 
brum, but  there  are  numerous  transverse  sulci  which  divide  and 
subdivide,  the  gray  matter  being  disposed  about  them  in  a  thin 
layer.  This  causes  a  section  of  the  organ  to  have  a  peculiar  tree- 
like appearance,  which  originates  the  name,  "  arbor  vitge,"  given  to 
the  cortical  matter  of  the  cerebellum.  Besides  this,  there  is  a  cen- 
tral collection  of  gray  substance — the  corpus  dentatum. 

What  peculiarities  does  the  gray  matter  of  the  cerebellar  cor- 
tex possess  ? 

Under  the  microscope  it  is  found  to  consist  of  three  layers  (Fig.  37). 
The  outer  is  a  layer  of  delicate  connective  tissue  which  supports 
fine  nerve-fibres  and  small  spindle-shaped,  branching  nerve-cells. 
The  middle  layer  is  characterized  by  irregularly  disposed  large  gan- 
glion-cells, and  the  branching  processes  from  these  ramify  in  the 
superficial  layer.  These  cells  are  known  as  Purkiuje's  cells.  The 
inner  layer  is  made  up  of  a  mass  of  small  spheroidal  cells,  and 
gradually  merges  into  the  white  substance. 

What  is  the  function  of  the  cerebellum  ? 

The  cerebellum  seems  to  exert  no  influence  upon  the  sensory 


TIIK   CEREBELLUM. 
Fio.  37. 


131 


Vertical  Section  tliidUirh  the  Cray  Matter  of  the  Iliiman  CerebeHum  (magnified  about 
llH)  flinnietors  :  Klein  and  Nuble  Smith):  «,  the  external  trray  or  cellular  layer;  b, 
corpuscles  of  I'urkinje;  '■,  internal  rust-colored  jrranular  layer;  </,  white  substance. 
Two  branched  capillaries  are  seen  at  the  upper  part  passing  into  the  gray  matter 
from  the  pia  mater. 


132  NERVOUS   SYSTEM. 

nerves,  for  sensibility  is  not  aiFeeted  by  its  injury  or  disease. 
The  motor  system  is,  however,  entirely  disorganized  by  lesions 
of  the  organ.  Co-ordination  of  the  voluntary  muscles  is  accom- 
plished by  this  portion  of  the  brain,  and  it  is  originated  in  the  gray 
matter  of  the  part.  It  has  no  effect  upon  the  senses  or  upon  the 
intellect,  so  far  as  is  known. 

What  is  the  effect  of  removing  the  cerebellum  in  animals  ? 

When  small  portions  are  removed  the  animals  become  feeble  and 
uncertain  in  their  movements,  but  are  able  to  move  for  ordinary 
purposes.  As  the  amount  removed  increases  the  want  of  co-ordi- 
nation of  the  voluntary  muscles  increases.  With  the  entire  cere- 
bellum gone  the  condition  is  absolute — animals  cannot  stand  or 
walk  or  bring  any  of  the  muscles  into  orderly  action.  If  the  ani- 
mal is  laid  upon  the  back,  it  cannot  recover  itself,  but  struggles 
vaguely  in  the  attempt.  The  senses  are  apparently  normal  and  the 
will-power  is  present :  if  a  blow  is  threatened,  an  attempt  is  made 
to  avoid  it.  When  the  lesion  is  confined  to  one  hemisphere,  the 
lack  of  co-ordination  is  noticed  in  the  opposite  half  of  the  body. 
Under  these  circumstances  the  animals  are  apt  to  fall  to  the  oppo- 
site side  and  roll  over  and  over  rapidly.  Such  movements  are 
known  as  forced  movements.  This  condition  may  persist  for  several 
days.  Pigeons  from  which  the  cerebellum  is  removed  may  live  for 
a  considerable  time,  sometimes  for  several  months,  after  the  opera- 
tion. In  some  cases  there  is  a  return  of  power  to  co-ordinate,  after 
partial  removal,  at  the  end  of  some  days. 

THE   CRANIAL  NERVES. 
What  are  the  cranial  nerves? 

They  are  a  set  of  twelve  pairs  of  nerves  which  arise  from  the 
brain.  They  are  varied  in  their  functions,  but  all  arise  from  gan- 
glia of  gray  matter  in  the  brain  and  medulla.  The  floor  of  the 
fourth  ventricle  is  particularly  rich  in  nuclei  in  which  these  cranial 
nerves  originate. 

How  may  the  cranial  nerves  be  classified  ? 

1.  In  the  order  of  their  emergence,  by  numbers:  (I)  Olfactory; 
(II)  Optic  ;  (III)  Motor  oculi ;  (IV)  Patheticus ;  (V)  Trigeminus ; 
(VI)  Abducens;  (VII)  Facial;  (VIII)  Auditory;  (IX)  Glosso- 
pharyngeal ;  (X)  Pneumogastric ;   (XI)  Spinal  accessory ;  (XII) 


THE  CRANIAL   NERVES.  133 

Hypoglossal. -f^  In  the  relation  of  their  functions  they  may  be 
arranged  as  nerves  of  special  sense,  nerves  of  common  sensation, 
motor  nerves,  and  mixed  nerves  (t.  e.  both  sensory  and  motor). 

r  (I)  olfactory,  (II)    optic,   (VIII)  audi- 
Nerves  of  special  sense,  <        toryj-,  and   parts   of  (V)  trigeminus 

(^       and  (IX)  glusso-pharyngeal. 
Nerves  of  common  sen-   (  The  greater  portion  of  the  (V)  trigem- 
sation,  |       inus. 

f  (III)  motor  oculi,  (lY)  patheticus,  (V) 

■,r  i  lesser  division  of  the  trigeminus,  (VI) 

Motor  nerves,  <         ,  ^  /^riT\.p    ■  i        i /vtt\  v, 

'  I        abducens.  (VH)  lacial,  and  (XII)  hy- 

[       poglossal,  (XI)  spinal  accessory  (?). 
Mixed  nerves,  \  ^^^>  glosso-pharyngeal  and  (X)  pneu- 

'  (       mogastric. 

What  is  the  distribution  of  the  motor  oculi  or  third  nerve? 

It  arises  from  a  nucleus  of  gray  matter  just  in  front  of  the  me- 
dulla, beneath  the  iter  e  tertio  ad  quartum  ventriculum,  passing 
out  through  the  crus  cerebri,  and  emerging  from  the  skull  in  the 
orbit.  It  gives  ofi"  some  fibres  to  the  lenticular  ganglion.  It  is 
distributed  to  all  the  muscles  of  the  eyeball,  with  the  exception 
of  the  superior  oblique  and  the  external  rectus  muscles.  It  also 
supplies  the  levator  palpebral  superioris  muscle,  and  by  its  con- 
nection with  the  lenticular  ganglion  controls  the  ciliary  and  pupil- 
lary muscles. 

What  is  the  function  of  the  third  nerve  ? 

It  is  a  purely  motor  nerve.  Its  function  is  best  described,  per- 
haps, by  showing  the  paralyses  which  follow  its  division  :  by  par- 
alysis of  the  elevator  of  the  upper  lid  we  have  jyfosis ;  by  the 
paralysis  of  the  muscles  of  the  eyeball  we  have  inability  to  move 
the  organ  up  or  down  or  inward  ;  by  the  unopposed  action  of  the 
external  rectus  the  eyeball  becomes  turned  outward  (external  stra- 
bismus) ;    by  the  action   upon   the  miiscle  of   the   iris   the  pupil 

*  A  convenient  old  medical-school  mnemonic  is  useful  in  remembering  the 
names  and  order  of  these  nerves — viz.  On  Old  Moriah's  Pointed  Top  A 
French  And  German  Picked  Some  Hops,  tlie  initial  letter  of  each  word  giv- 
ing the  key.     It  is  given  witli  an  apology  to  many  generations. 

t  Of  the  nerves  of  special  sense,  ( [)  olfactory,  ( II )  optic,  and  (VIII)  audi- 
tory will  be  explained  later,  and  may  be  omitted  from  further  consideration 
for  the  present. 


134  NERVOUS  SYSTEM. 

remains  dilated  and  does  not  respond  to  light ;  and  by  the  paraly- 
sis of  the  ciliary  muscle  the  accommodation  of  the  lens  for  near 
vision  is  prevented.  The  control  of  the-  pupil  is  not  a  voluntary 
one ;  but  the  effect  of  a  strong  voluntary  effort,  exerted  through 
the  third  nerve,  shows  itself  in  contraction  of  the  pupil,  as  when 
the  eyeball  is  turned  strongly  inward  and  upward. 

Describe  and  give  the  function  of  the  patheticus  or  fourth  cra- 
nial nerve. 

It  arises  close  by  the  third  nerve  beneath  the  aqueduct  of  Syl- 
vius, and  emerges,  after  decussation,  from  the  valve  of  Vieussens. 
Thence,  passing  around  the  crus  cerebri,  it  runs  parallel  with  the  mo- 
tor oculi  (third)  nerve  to  the  orbit,  where  it  is  supplied  to  the  supe- 
rior oblique  muscle.  Its  paralysis  prevents  the  muscle  from  main- 
taining the  horizontal  plane  of  the  eyeball.  If  this  paralysis  occurs, 
there  is  double  vision,  and  the  image  seen  by  the  affected  eye 
appears  oblique  and  inferior  to  the  image  of  the  other  eye.  This 
may  be  corrected  by  inclining  the  head  to  "the  opposite  side.  This 
jierve  is  also  known  as  the  trochlearis  or  trochlear  nerve. 

What  is  the  course  and  function  of  the  sixth  or  abducens  nerve  ? 

It  arises  from  a  nucleus  of  gray  matter  in  the  floor  of  the  fourth 
ventricle,  and  its  nucleus  is  connected  with  those  of  the  third,  fourth, 
and  seventh  nerves.  It  emerges  without  decussation  at  the  poste- 
rior border  of  the  pons  Varolii,  and  passes  forward  to  the  orbit 
with  the  third  and  fourth  nerves.  In  its  course  it  has  many  com- 
munications with  the  sympathetic  nerves,  but  their  significance  is 
unknown.  It  is  supplied  to  the  external  rectus  muscle  of  the  eye, 
and  its  stimulation  causes  external  squint,  and  paralysis  causes 
internal. 

What  is  the  origin  of  the  trigeminus  or  fifth  nerve  ? 

This  nerve  resembles  the  spinal  nerves  in  having  a  motor  and  a 
sensory  root,  the  latter  possessing  a  ganglion  (Gasserian).  The 
origin  of  the  nerve  seems  to  be  in  centimes,  separate  for  motor  and 
sensory,  in  the  floor  of  the  fourth  ventricle.  There  are  fibres  which 
join  the  trunk  of  the  nerve  which  are  derived  from  the  spinal  cord 
and  from  the  cerebellum.  It  emerges  from  the  pons  Varolii  as  two 
distinct  nerve-roots.  The  larger  of  the  two,  the  sensory,  soon  enters 
the  Grasserian  ganglion,  the  motor  root  passing  beneath  without 
communication.  The  nerve  then  breaks  up  into  three  branches : 
of  these  the  first  and  second  are  formed  entirely  from  the  sensory 


THE   CRANIAL    NERVES. 


135 


root,  ^vhilc  the  third  carries  all  the  iiuitor  fibres,  and  with  them  some 
of  the  sensory,  so  that  the  third  branch  of  the  nerve  is  partly  sen- 


FiG.  38. 


Diagram  of  the  Fifth  Nerve  and  its  Distribution  ;  1,  sensitive  root ;  2,  motor  root;  3,  Gas- 
serian  ganglion ;  I,  ophthalmic  division ;  11,  superior  maxillary  division  ;  III,  infe- 
rior maxillary  division;  4,  supraorbital  nerve,  distributed  to  the  skin  of  the  fore- 
head, inner  angle  of  the  eye,  and  root  of  the  nose;  o,  infraorbital  nerve,  to  the  skin 
of  the  lower  eyelid,  side  of  the  nose,  and  skin  and  mucous  membrane  of  the  upper 
lip;  6,  mental  nerve,  to  the  integument  of  the  chin  and  edge  of  the  lower  jaw,  and 
skin  and  mucous  membrane  of  the  lower  lip  ;  «,  n,  external  terminations  of  the  na^al 
branch  of  the  ophthalmic  division,  to  the  mucous  membrane  of  the  inner  part  of  the 
eye  and  the  nasal  passages,  and  to  the  base,  tip,  and  wing  of  the  nose;  t,  temporal 
branch  of  the  superior  maxillary  division,  to  the  skin  of  the  temjioral  region  ;  m, 
malar  branch  of  the  superior  maxillary  division,  to  the  .skin  of  the  cheek  and  neigh- 
boring parts;  h,  buccal  branch  of  the  inferior  maxillary  division,  passing  along  the 
surface  of  the  buccinator  muscle,  and  distributed  to  the  mucous  membrane  of  the 
cheek  and  to  the  mucous  membrane  and  skin  of  the  lips;  I,  lingual  nerve,  to  the 
mucous  membrane  of  the  anterior  two-thirds  of  the  tongue;  a/,  auriculo-temporal 
branch  of  the  inferior  maxillary  division,  to  the  skin  of  the  anterior  part  of  the 
external  ear  and  adjacent  temporal  region  ;  x,  x,  x.  muscular  branches,  to  the  tem- 
poral, masseter,  and  internal  ■■•ud  external  pterygoid  muscles;  y,  muscular  branch, 
to  the  mylo-hyoid  and  anterior  belly  of  the  diagastric ;  /,  sensitive  branch  of  com- 
munication to  the  facial  nerve. 


sory  and  partly  motor.     There  is  a  partial  decussation  of  the  fibres 
in  the  medulla,  but  many  pass  direct  to  the  same  side. 

What  muscles  are  supplied  by  the  motor  root? 

The  7nHKcIeF:  of  vidsticdtiou.     The  temporal,  masseter,  and  both 
pterygoid  muscles,  as  well  as  the  anterior  belly  of  the  digastric 


136  NERVOUS   SYSTEM. 

muscle  and  the  mylo-hyoid,  receive  their  innervation  from  the  motor 
root  of  the  fifth  nerve.  Besides  this,  the  tensor  palati  and  tensor 
tympani  muscles  are  supplied  by  this  nerve  through  its  communi- 
cation with  the  otic  ganglion  of  the  sympathetic  system.  A  branch 
to  the  buccinator  muscle  is  probably  not  motor,  but  sensory.  Le- 
sions of  the  nerves  paralyze  these  muscles. 

What  is  the  distribution  of  the  sensory  root  ? 

The  sensory  fibres  of  the  fifth  nerve  are  distributed  in  all  three 
branches,  and  supply  sensation  to  the  skin  of  the  face  and  anterior 
portion  of  the  head,  emerging  from  the  bony  canals  upon  the  face 
at  the  supraorbital,  infraorbital,  and  mental  foramina ;  it  is  also 
supplied  to  the  mucous  membrane  of  the  mouth  and  tongue  (by 
the  lingual  branch)  and  to  the  muscles  of  the  part. 

What  results  follow  division  of  the  sensory  root  of  the  fifth  nerve  ? 
There  is  complete  anaesthesia  of  the  skin  and  mucous  membranes 
of  the  face. 

What  is  the  trophic  influence  of  this  nerve-root  ? 

It  is  of  very  great  value.  If  it  be  divided,  the  complete  anaes- 
thesia of  the  conjunctiva,  of  the  nostrils,  and  of  the  lips  prevents 
the  reflex  self-protection  vrhich  belongs  to  the  parts,  and  they  be- 
come injured  very  easily.  Aside  from  that,  the  direct  influence 
upon  all  the  parts  is  great,  so  that  vphen  it  is  cut  off  there  is  a 
rapid  degeneration  resulting,  vphich  is  specially  apparent  in  the 
mucous  membrane  of  the  nose  and  in  the  cornea. 

What  influence  has  the  sensory  branch  upon  the  special  senses  ? 
(1)  Its  division  causes  total  anaesthesia  to  the  skin  and  mucous 
membrane ;  the  loss  of  the  sense  of  touch  in  the  part  is  of  great 
importance,  for  the  tongue  and  lips  are  used  much  for  this. 
(2)  Upon  the  sense  of  sight  it  has  a  very  controlling  influence, 
for,  as  we  have  seen,  the  trophic  influence  is  essential  to  the 
maintenance  of  the  integrity  of  the  eye.  (3)  Upon  the  sense  of 
smell.  Here  the  influence  is  the  same  as  with  the  eyes,  trophic. 
The  smell  is  soon  lost  on  account  of  degeneration  of  the  mucous 
membrane  after  division  of  the  fifth  nerve.  (4)  Taste,  prob- 
ably, is  not  a  direct  function  of  the  nerve,  but  if  the  tactile  sensi- 
bility is  gone  and  the  trophic  changes  are  begun,  the  sense  of  taste 
soon  disappears  in  the  anterior  portion  of  the  tongue.  (5)  Upon 
the  hearing  the  effect  is  more  gradual  and  less  distinct.    The  seere- 


TIIK   CRANIAL   NERVES. 


137 


tioiis  of  the  cavity  of  the  tyiiipanuin  and  of  the  external  auditory 
canal  are  of  great  importance  in  niaintaining  normal  conditions. 
They  arc  under  the  trophic  influence  of  the  fifth  nerve,  both 
throunh  its  auriculo-temporal  branch  and  through  its  communica- 
tion with  the  otic  ganglion.  The  tensor  tympani  muscle  is  also 
supplied  by  the  motor  root.  Thus,  the  auditory  apparatus  is  con- 
siderably under  the  control  of  the  nerve. 

What  painful  afifections  belong  to  this  nerve? 

Headaches  of  the  scalp  and  deeper  tissues,  and  more  especially 
the  frontal  sinuses,  are  common.     Toothache  and  facial  neuralgia 


Fui.  39. 


Diagram  of  the  Facial  Nerve  and  its  Distrilnition  :  1,  Facial  nerve  at  its  entrance  into  the 
internal  auditory  meatus ;  2,  its  exit  at  the  stylo-niastoid  foramen  ;  3,  4,  teni|i(iral  and 
posterior  auricular  brandies,  distributed  to  the  muscles  of  the  external  ear  and  to  the 
occipitalis;  o,  branches  to  tlie  frontalis  muscle;  0,  branches  to  the  stylo-hyoid  and 
digastric  muscles;  7,  branches  to  the  upper  part  of  the  platysma  myoides;  .s,  branch 
of  coninuinicatiou  with  the  superficial  cervical  uerve  of  the  cervical  plexus. 

are  due  to  irritation  or  disease  of  parts  of  the  nerves.  Tic  dou- 
Ivurcux  is  a  persistent  neuralgia  of  some  or  all  of  the  branches  of 
the  nerve. 


138  NEEVOUS   SYSTEM. 

What  is  the  origin  of  the  facial  or  seventh  nerve  ? 

It  arises  in  the  floor  of  the  fourth  ventricle,  and  its  fibres  emerge 
at  the  edge  of  the  pons  Varolii  in  company  with  the  (eighth) 
auditory  nerve  (sometimes  known  as  the  portio  mollis  ;  the  facial 
being  then  called  the  portio  dura  of  the  seventh  pair,  when  the 
classification  of  the  cranial  nerves  is  made  into  nine  pairs).  It 
passes  into  the  internal  auditory  canal,  and  escapes  from  the 
skull  by  way  of  the  aqueduct  of  Fallopius  and  the  stylo-mastoid 
foramen. 

How  is  the  facial  nerve  distributed? 

It  is  almost  wholly  a  motor  nerve,  and  is  distributed  to  all  of  the 
muscles  of  the  face  (Fig.  39)  except  those  mentioned  as  controlled 
by  the  motor  branch  of  the  trigeminus  nerve.  The  muscles  of  the 
eyelids  and  the  muscles  of  the  palate  in  part  are  innervated  by  it, 
as  well  as  the  parotid  and  mhmaxillary  glands^  through  the  chorda 
tympani.  In  the  neck  it  supplies  the  posterior  belly  of  the  digas- 
tric and  the  platysma  myoides  muscles.  It  also  sends  branches  to 
the  stapedius  muscle  of  the  internal  ear  and  to  all  of  the  muscles 
of  the  external  ear.  The  branches  passing  to  the  salivary  glands 
are  secretory  in  their  function  ;  and  this  is  the  only  exception  to 
the  motor  influence  of  the  nerve. 

What  is  the  function  of  the  facial  nerve  ? 

It  is  the  motor  nerve  which  parallels  in  its  distribution  the 
sensory  root  of  the  fifth  ;  it  supplies  the  superficial  muscles,  as  the 
latter  does  the  skin.  It  is  the  nerve  of  expression,  by  which  the 
features  are  made  to  reflect  the  emotions. 

What  is  the  effect  of  paralysis  of  this  nerve  ? 

If  the  nerve  be  divided  or  diseased,  the  face  of  that  side  is 
devoid  of  motion  (Fig.  40),  and  becomes  smooth  and  expression- 
less, while  the  sound  side  is  held  in  its  customary  pose.  The 
eyelids  cannot  close  themselves,  and  the  lips  do  not  oppose  properly, 
on  account  of  the  defective  action  of  the  orbicular  muscle.  There 
is  difficulty  in  drinking  and  in  articulation  for  the  same  reason. 

State  what  influence  is  ascribed  to  the  chorda  tympani  branch. 

The  chorda  tympani  is  a  small  filament  given  off"  from  the  facial 
in  the  aqueduct  of  Fallopius,  some  of  whose  fibres  are  distributed  to 
the  submaxillary  gland.  If  this  nerve  be  divided,  the  secretion  of 
saliva  from  the  gland  is  greatly  diminished,  while  stimulation  of  the 


THE   CRANIAI>   NEKVKS. 


139 


norvo  will  excite  a  copious  flow.  This  is  an  active  secretion,  ami  is 
nut  a  sinipli'  filtration  clue  to  vaso-uiotor  chanfrcs.  A  similar  influ- 
ence is  noted  in  the  corresponding  hall"  of  the  tongue.  There  is  a 
similar  distribution  of  tibres  from  the  facial  to  the  parotid  gland 


Fig.  40. 


Facial  Paralysis  of  the  Right  Side. 

through  the  lesser  petrosal  nerve,  but  their  action  has  not  been  so 
thoroughly  analyzed  as  in  the  case  of  the  submaxillary  and  chorda 
tynipani. 

The  chorda  tympani  has  still  further  an  effect  upon  the  sense  of 
taste  in  the  anterior  portion  of  the  tongue.  If  it  be  divided,  the 
taste  is  much  blunted  on  the  aff'ected  ,side.  It  is  not  known  if  this 
be  due  to  the  communication  of  the  glosso-phai'vngeal  or  not,  but 
it  seems  probable  that  it  cannot  be  ascribed  to  either  the  trifacial 
or  facial  alone  ;  and  it  is  considered  to  be  a  plausible  explanation 
tliat  the  chorda  tympani  does  bear  some  fibres  of  the  glosso- 
pharyngeal. 


140  NERVOUS   SYSTEM. 

Why  is  not  the  ocular  paralysis  of  the  seventh  nerve  as  serious  as 
that  of  the  fifth  ? 

The  eyelids  remain  open  in  facial  paralysis,  and  the  conjunctiva 
is  subject  to  injury  by  drying. and  by  foreign  bodies  ;  but  the  injury 
is  not  so  great  as  in  paralysis  of  the  fifth  nerve,  because  the  seventh 
has  no  trophic  influence. 

What  is  the  origin  of  the  glosso-pharyngeal  or  ninth  nerve  ? 

It  arises  in  the  medulla  from  centres  near  those  for  the  vagus 
and  spinal  accessory  nerves.  Its  fibres  pass  through  the  substance 
of  the  medulla  and  em^erge  in  company  with  those  of  the  vagus  and 
spinal  acessory  to  pass  with  them  from  the  skull  through  the  jug- 
ular foramen.  It  gives  off"  a  small  branch  which  passes  to  the 
tympanum  and  Eustachian  tube  (Jaeobson's  nerve)  while  in  the 
jugular  foramen,  and  presents  a  small  ganglion,  the  petrosal ;  and 
it  has  communicating  branches  to  the  seventh  and  tenth  nerves 
and  to  the  otic  ganglion.  It  divides  as  it  passes  down,  one  branch 
passing  forward  to  the  tongue,  and  one  going  to  the  pharynx 
(whence  its  name). 

How  is  the  glosso-pharyngeal  distributed  ? 

The  portion  which  passes  to  the  tongue  is  distributed  to  the  pos- 
terior portion  of  the  organ,  to  the  circumvallate  papillae,  and  the 
mucous  membrane  behind  them,  some  fibres  going  to  the  lining  of 
the  soft  palate,  pillars  of  the  fauces,  and  tonsils.  The  other  branch 
is  distributed  to  the  mucous  membrane  of  the  pharynx,  and  by 
direct  branches  and  communications  with  other  nerves  to  all  the 
muscles  involved  in  swallowing. 

What  is  the  function  of  the  glosso-pharyngeal  nerve  ? 

(1)  It  is  the  nerve  of  taste;  and  (2)  it  is  essentially  a  nerve  of 
deglutition. 

Explain  the  action  of  the  glosso-pharyngeal  as  a  nerve  of  taste. 

It  is  only  in  the  latter  part  of  the  stay  of  food  in  the  mouth  that 
it  reaches  the  region  supplied  by  this  nerve.  When  the  food  is  to 
be  swallowed,  it  is  pressed  by  the  base  of  the  tongue  against  the 
palate  arch  and  pushed  into  the  pharynx.  It  is  then  that  the  sense 
of  taste  is  exercised  here.  The  reflex  stimuli  then  excited  start  up 
the  motor  chain  which  pushes  the  bolus  on  to  the  stomach.  As 
already  said,  there  is  considerable  question  as  to  whether  the  tri- 
geminal or  glosso-pharyngeal  is  really  the  conductor  of  this  sense, 
but  it  is  quite  likely  that  both  are  essential. 


THE   CRANIAL   NERVES.  141 

What  is  the  function  of  the  glosso-pharyngeal  as  a  motor  nerve  ? 

\\  lic'tlicr  l)y  reason  of  its  coinuiiiiiifalioiis  with  otlier  nerves  or 
not  ill  its  distril)utioii,  tlie  nerve  is  a  motor  nerve  as  well  as 
sensory.  Its  distribution  is  to  all  the  muscles  of  deglutition, 
and  stimulation  causes  contraction  of  the  muscles,  while  division 
paralyzes  them.  The  very  numerous  connections  of  the  nerve  com- 
plicate its  anatomical  origin  very  greatly,  and  interfere  with  a  clear 
comprehension  of  the  unaided  function  of  the  nerve. 

Where  does  the  reflex  for  swallowing  originate? 

In  the  medulla  oblongata,  where  the  centre  of  origin  of  the  nerve 
is  situated. 

What  is  the  origin  of  the  pneumogastric  or  tenth  nerve  ? 

It  arises  from  the  gray  matter  in  tlie  floor  of  the  fourth  ventri- 
cle, its  nucleus  being  very  close  to  those  of  the  glosso-pharyngeal, 
spinal  accessory,  and  hypoglossal.  Its  fibres  pass  through  the  sub- 
stance of  the  medulla  oblongata,  and  emerge  from  its  lateral  sur- 
face with  the  roots  of  its  associate  nerves,  the  glosso-pharyngeal 
and  spinal  accessory.  It  passes  from  the  skull  with  them  by  the 
jugular  foramen.  It  has  at  this  point  a  ganglionic  enlargement. 
From  here  it  passes  down  the  neck,  and  is  distributed  more  diflFusely 
than  any  other  cranial  nerve. 

What  synonyms  has  the  tenth  nerve? 

Pneumogastric,  from  its  distribution  and  function  ;  vagus  or  Par 
Vagum,  from  its  scattered  distribution  («<_(/««,  Latin  =  wanderer). 

What  principal  distributions  has  the  pneumogastric? 

It  is  supplied  to  the  organs  by  which  air  and  food  enter  the  body, 
and  besides  this  has  several  important  connections  with  the  s^'mpa- 
thetic  system.  (1)  To  the  larynx  it  supplies  sensation  and  motion 
through  the  superior  and  inferior  lari/iigeal  branches.  (2)  In  the 
chest  it  forms  the  pidmonari/  plexuses,  which  innervate  the  bronchi 
and  lungs.  (3)  Branches  to  the  cardiac  plexus  supply  important 
stimuli  to  the  heart  and  great  vessels.  (4)  There  are  branches  to 
the  2)har?/nffeal  and  asopluigeal  plexuses  which  are  both  sensor)'  and 
motor,  supplying  both  the  mucous  membrane  and  the  muscular 
structures  of  the  parts.  (5)  Its  terminal  branches  supply  the  sen- 
sory and  motor  nerves  to  the  stomach,  the  left  nerve  being  dis- 
tributed on  its  anterior  wall,  and  the  right  posteriorly.    (G)  Branches 


142  NERVOUS  SYSTEM. 

also  pass  to  tlie  liver  and  spleen  and  communicate  with  the  solar 
plexus. 

Mention  some  of  its  communications  with  other  nerves. 

Soon  after  leaving  its  origin  in  the  medulla  the  vagus  enters  into 
so  many  communications  with  other  nerves,  both  sensory  and  mo- 
tor, that  it  is  difficult  to  know  the  real  fibres  of  the  original  root 
and  to  determine  what  are  original  and  what  derived  functions. 
The  sympathetic  system  sends  fibres  in  all  the  branches  of  the 
pneumogastric,  and  the  pneumogastric  sends  branches  to  many  of 
the  important  sympathetic  plexuses  and  ganglia ;  the  pharyngeal, 
laryngeal,  oesophageal,  pulmonary,  cardiac,  and  solar  plexuses  are 
so  made  up  by  branches  from  both.  The  spinal  accessory  nerve  is 
an  important  contributor,  in  that  it  sends  a  large  branch  which  is 
incorporated  in  the  vagus.  There  are  also  communications  to  the 
glosso-phai'yngeal  and  hypoglossal  nerves,  and  it  also  receives 
motor  fibres  from  the  facial  and  upper  two  cervical  nerves.  The 
original  nerve  is  probably  entirely  sensory,  and  its  motor  function 
is  derived  from  these  connections  with  motor  nerves. 

Where  are  the  motor  fibres  from  the  spinal  accessory  nerve  sup- 
posed to  be  distributed? 

Principally  in  the  recurrent  laryngeal  nerve. 

What  is  the  function  of  the  vagus  in  connection  with  respira- 
tion ? 

The  nerve  supplies,  as  has  been  said,  the  motor  and  sensory 
functions  of  the  larynx,  and  in  this  is  of  value  to  the  respiratory 
function  both  in  the  prevention  of  foreign  substances  entering  the 
rim  a  glottidis,  and  in  the  opening  of  that  orifice  for  the  entrance 
of  air.  Besides  this,  it  supplies  sensory  fibres  to  the  pulmonary 
plexus  which  transmit  the  reflex  stimulus  to  the  medulla,  by  which 
the  motor  apparatus  is  excited  to  action. 

What  is  its  influence  upon  the  voice? 

The  muscles  of  the  larynx  involved  in  the  production  of  sound 
are  supplied  by  this  nerve,  and,  as  the  approximation  of  the  chor- 
dae vocales  is  necessary  for  this,  it  follows  that  the  voice  is  depend- 
ent upon  the  fibres  of  the  pneumogastric  supplied  by  the  inferior 
or  recurrent  laryngeal  nerve. 

What  effect  upon  respiration  follows  section  of  the  vagi  ? 

The  respiration  is  slowed  immediately  to  about  half  its  usual 


THK   CRANIAL   NERVES.  143 

rate,  ami  soon  drops  to  five  or  six  to  tlu;  niinuto,  and  oven  slower. 
Tlie  respiration  is  easy — inspiration  slow  and  full,  ex])iration  harsh 
and  sudden.  Death  follows  this  operation  in  a  short  time  (one  to 
six  days),  and  the  animal  during-  the  time  is  sluggish  and  appa- 
rently suffers  from  slow  earbonic-oxide  nareosis.  It  is  inferred 
iVom  this  that  the  vagus  is  the  nerve  which  carries  to  the  auto- 
matic centre  the  stimuli  which  arc  needed  to  keep  up  the  automat- 
ism, and  that  the  medulla  is  incapable  of  originating  the  motor 
impulses  unless  controlled  by  afferent  stimuli. 

What  is  the  function  of  the  pneumogastric  in  deglutition  ? 

Deglutition  both  in  the  pharynx  and  oesophagus  is  under  the  influ- 
ence of  the  vagus,  which  gives  innervation  directly  to  the  thoracic 
part  of  the  latter  and  through  the  inferior  laryngeal  branch  to  the 
cervical  part.  The  sensory  fibres  act  as  conductors  of  the  stimulus 
Avhieli  results  in  the  reflex  peristalsis  by  which  the  food  is  carried 
on  through  the  cesophagus.  The  sensory  distribution  to  the  larynx 
must  not  be  forgotten  in  this  connection,  for  by  it  food  is  kept  from 
the  respiratory  organs.  Section  of  the  vagi  causes  paralysis  of 
swallowing,  and  food  is  apt.  to  pass  the  glottis  on  an  attempt  to 
swallow,  not  even  a  cough  being  excited  by  such  an  accident.  The 
closure  of  the  glottis  in  swallowing  is  caused  by  a  reflex  action 
known  as  the  "  action  of  arrest,"  and  is  derived  from  the  sensory 
fibres  of  the  vagus. 

What  is  the  physiological  relation  of  this  nerve  to  the  stomach  ? 

Both  sensory  and  motor.  The  stomach  receives  its  warning  of 
the  presence  of  food  through  the  sensory  fibres,  and  the  muscular 
fibres  excite  the  organ  to  contract  upon  it  and  "  churn  "  it  about 
during  digestion.  There  is  also  a  vaso-motor  influence  derived 
from  the  vagus.  When  the  nerve  is  cut  but  little  food  can  reach 
the  stomach  because  of  the  paralysis  of  the  oesophagus,  and  what 
food  does  enter  is  digested  very  slowly,  so  that  the  function  of  the 
pneumogastric  may  be  considered  essential  to  stomach  digestion. 
The  connection  with  the  solar  plexus  also  involves  the  intestines  in 
the  action  of  the  vagus. 

What  important  excito-motor  reflexes  depend  upon  the  pneumo- 
gastric for  one  or  both  stimuli? 

Coughing  and  vomiting,  as  well  as  many  other  less  essential 
reflexes,  such  as  sighing,  hiccoughing,  and  the  like. 


144  NERVOUS  SYSTEM. 

What  is  the  influence  of  the  vagus  upon  the  heart  ? 

There  are  numerous  branches  to  the  cardiac  plexus  from  the 
trunk  of  the  vagus  and  from  its  inferior  laryngeal  branch.  Stim- 
ulation of  the  pneumogastric  nerve  diminishes  the  frequency,  or, 
if  strong,  entirely  stops  the  heart  in  diastole.  The  nerve  is  there- 
fore regarded  as  having  an  inhibitory  action.  This  is  an  unusual 
effect,  for  in  other  cases  the  stimulation  of  nerves  going  to  muscles 
causes  contraction :  the  heart,  however,  becomes  flaccid  under  the 
influence  of  the  stimulated  vagus. 

What  is  the  origin  of  the  spinal  accessory  or  eleventh  cranial 
nerve  ? 

It  is  twofold.  One  root  arises  in  the  gray  matter  of  the  medulla 
near  the  nucleus  for  the  vagus,  while  the  others  arise  from  the 
lateral  tract  of  the  cord  as  low  as  the  fifth  or  sixth  cervical  vertebra, 
and  pass  up  between  the  anterior  and  posterior  spinal  nerve-roots  to 
join  the  medullary  (or  accessory)  portion  at  its  emergence  from  the 
medulla.  The  united  nerve  passes  out  through  the  jugular  foramen 
with  the  glosso-pharyngeal  and  pneumogastric  nerves. 

How  is  the  nerve  distributed? 

Soon  after  leaving  the  skull  it  again  divides,  the  medullary  root 
joining  the  trunk  of  the  pneumogastric,  while  the  spinal  root  sup- 
plies the  sterno-mastoid  and  trapezius  muscles. 

What  is  the  function  of  the  spinal  accessory  nerve  ? 

The  nerve  is  a  motor  to  all  intents,  though  it  has  some  sensory 
fibres,  as  is  shown  by  the  pain  caused  by  pinching  it. 

(1)  The  anastomotic  branch^  which  joins  the  pneumogastric,  is 
apparently  largely  given  off  in  the  recurrent  laryngeal  nerve,  but 
its  section  does  not  produce  the  same  effect  upon  the  larynx  as 
section  of  the  trunk  of  the  vagus  or  of  its  inferior  laryngeal 
branch.  There  is  paralysis  of  the  voice,  but  not  of  the  move- 
ments of  the  glottis  for  respiration.  There  are  probably  some  fibres 
of  this  nerve  also  given  off  to  the  cardiac  plexus. 

(2)  The  muscular  branch  supplies  the  sterno-mastoid  and  trape- 
zius muscles,  but  these  muscles  are  also  supplied  by  the  cervical 
spinal  nerves,  and  their  action  is  not  paralyzed  by  the  section  of 
this  branch  of  the  spinal  accessory.  It  is  found,  however,  that 
the  relation  of  these  muscles  to  respiration  is  impaired  by  isolation 
from  this  nerve ;  that  is,  when  the  breath  is  held  in  any  violent 
exertion,  as  straining  or  pushing,  or  when  a  loud  cry  is  uttered, 


THE  SENSES.  145 

tlio  sterno-niastoid  aiul  trapezius  nmscles  contract  to  fix  the  head 
and  hold  the  spine  steady.  This  action  seems  to  be  prevented  by 
the  section  of  this  muscular  branch  of  the  spinal  accessory. 

What  is  the  origin  of  the  hypoglossal  or  twelfth  cranial  nerve  ? 

It  arises  in  the  gray  matter  at  the  inferior  extremity  of  the 
floor  of  the  fourth  ventricle,  near  the  origin  of  the  spinal  accessory 
and  pneumogastric  nerves.  The  fibres  pass  through  the  substance 
of  the  medulla  oblongata,  skirting  (and  perhaps  gaining  fibres  from) 
the  olivary  body,  and,  emerging  in  a  number  of  small  bundles, 
collect  into  a  nerve-trunk  which  emerges  from  the  skull  by  the 
anterior  condyloid  foramen. 

How  is  the  hypoglossal  nerve  distributed? 

It  passes  down  the  neck  to  about  the  level  of  the  hyoid  bone, 
where  it  curves  forward  and  into  the  tongue,  giving  off  branches  to 
the  muscles  which  move  that  organ. 

What  is  the  function  of  the  hypoglossal  nerve  ? 

It  is  a  motor  nerve,  but  possesses  some  sensory  fibres  derived 
from  the  cervical  spinal  nerves  and  from  the  trigeminus,  with 
whose  lingual  branch  it  inosculates  on  the  side  of  the  tongue. 
Filaments  from  it  are  distributed  to  all  the  muscles  which  move 
the  tongue,  and  to  the  depressors  of  the  hyoid  bone  through  its 
descending  branch. 

What  influence  has  this  nerve  upon  digestion? 

It  is  important  in  mastication,  for  its  muscles  move  the  food 
about  for  the  better  action  of  the  teeth.  In  animals,  after  division 
drinking  is  impossible,  because  they  are  unable  to  lap  up  fluids,  and 
the  food  is  swallowed  with  difficulty  because  it  is  not  carried  back 
into  the  pharynx  by  the  tongue  after  mastication. 

What  is  its  connection  with  speech? 

Articulation  of  most  sounds  involves  movements  of  the  tongue. 
Impaired  articulation  is  an  early  symptom  in  bulbar  or  glosso- 
labio-laryngeal  paralysis. 

THE  SENSES. 

What  organs  are  necessary  for  sensation? 

A  peripheral  organ  for  the  reception  of  an  impression,  a  nerve 
for  its  conduction,  and  a  centre  in  the  brain  for  the  perception. 
10— Phy. 


146  THE   SENSES. 

It  is  by  means  of  impressions  so  received  and  conducted  to  it  that 
the  mind  is  able  to  control  the  body  and  to  take  cognizance  of  the 
external  world. 

Into  what  classes  may  the  sensations  be  arranged  ? 

Common  sensations  and  special  sensations.  These  last  are  com- 
monly called  "  the  senses." 

What  is  meant  by  the  common  sensations? 

Such  perceptions  as  cannot  be  distinctly  located  in  any  organ  or 
set  of  organs,  such  as  fatigue,  hunger,  thirst,  satiety.  Besides  this, 
there  are  some  sensations  which  involve  certain  organs  which  must 
be  classed  under  this  head  ;  thus  inclinations  to  cough  or  to  sneeze 
or  to  vomit  are  common  sensations,  and,  similarly,  to  urinate  or 
defecate.  Many  of  these  sensations  occupy  a  border-line  between 
common  sensibility  and  the  special  sense  of  touch,  such  as  itching 
and  tickling. 

Is  pain  a  common  sensation? 

It  is,  but  is  very  closely  allied  to  the  sense  of  touch.  The  two 
may  be  differentiated,  however.  If  one  touch  a  sharp  instrument, 
he  may  perceive  its  shape  and  condition,  but  if  the  pressure  be 
increased  the  ability  to  perceive  its  form  is  lost,  and  instead  the 
sensation  of  pain  is  established.  The  relation  of  the  two  is  curi- 
ously shown  in  partial  anaesthesia  by  drugs,  as  when  one  takes 
nitrous-oxide  gas  for  the  extraction  of  a  tooth,  and  is  able  to  feel 
the  operation  and  to  know  what  has  been  done,  without  in  the  least 
feeling  pain. 

What  is  the  real  seat  of  the  senses  ? 

The  brain  or  sensormm.  The  organ  of  the  mind,  which  perceives 
the  thing  which  the  organ  of  sense  has  taken  an  impression  from, 
is  the  fundamental  structure  in  the  necessary  chain. 

What  is  hallucination? 

It  is  the  perception  of  an  object  as  a  real  presence  without  the 
presence  of  the  object  to  justify  the  perception  ;  that  is,  it  is  an 
act  of  the  brain  which  refers  its  action  to  an  organ  of  the  senses. 
Thus,  in  delirium  tremens  a  person  may  perceive  many  curious  and 
uncanny  things,  which  his  mind  hears  and  sees  and  feels,  but  which 
his  senses  could  not  take  cognizance  of,  because  they  are  only 
"  creatures  of  the  mind." 


TOUCH.  147 

Do  the  nerves  of  special  sense  possess  the  property  of  common 
sensibility  ? 

No.  Till!  six'cial  nerves  liave  no  other  function  than  tlic  special 
one  for  wliich  they  arc  set  apart ;  and  when  they  are  separated 
from  tlieir  special  organs  for  receiving  impressions,  they  no  hunger 
respond  to  the  customary  stimuli. 

What  are  the  special  senses? 

Touch,  taste,  smell,  hearing,  and  sight. 

TOUCH. 
What  is  the  organ  of  touch  ? 

The  skin  and  the  mucous  membranes  adjoining  it.  The  nails 
and  teeth  too  exercise  a  peculiar  function  in  this  regard,  and  the 
hair  in  some  regions — e.  g.  eyelashes.  The  sensations  of  touch  are 
communicated  to  the  central  nervous  system  through  the  agency 
of  the  sensory  nerves  of  the  spinal  and  cranial  systems. 

What  varieties  of  the  sense  of  touch  are  found  ? 

(1)  Tactile  sensibility,  or  touch  proper;  (2)  the  sense  of  pressure 
or  weight ;  (H)  the  sense  of  temperature.  All  of  these,  when  car- 
ried beyond  moderate  limits,  are  merged  into  the  sensation  of  pain. 

What  factors  determine  the  acuteness  of  touch  ? 

The  (Jisfribiifioii  of  the  eud-orgmis  of  the  sensory  nerves  varies  in 
different  parts  of  the  body,  and  the  more  numerous  the  touch-cor- 
puscles, the  more  acute  the  sensibility  of  the  part.  Again,  the 
thickness  of  the  epidermis  has  marked  influence  in  determining  the 
tactile  ability,  portions  of  the  hands  and  feet,  when  callous,  having 
very  blunted  sensibility. 

What  qualities  of  bodies  are  determined  by  touch  ? 

Their  hardness  and  elasticit}',  the  quality  of  tlie  surface  as  to 
smoothness,  the  size  and  form  and  the  temperature  and  wet  or  dry 
condition,  are  all  easily  determined  by  touch. 

Why  is  the  hand  of  especial  value  as  an  organ  of  touch  ? 

Jiocausc  of  the  acuteness  of  its  sensibility.  Further  than  this, 
it  is  so  constructed  as  to  be  capable  of  forming  impressions  of 
bodies  by  reason  of  its  power  to  grasp  them  and  to  test  them  as 
to  weight. 


148 


THE  SENSES. 


How  is  the  acuteness  of  touch  measured  ? 

By  means  of  a  pair  of  compasses  whose  points  are  blunted.  The 
legs  of  the  instrument  are  separated,  and  the  distance,  between 
the  points  which  can  jvist  be  distinguished  as  two  separate  con- 
tacts, measures  the  sensibility.  From  the  accompanying  table  it 
will  be  seen  that  the  touch  is  most  acute  in  the  tip  of  the  tongue 
and  in  the  fingers  and  tips,  while  in  other  portions  the  sense  of 
touch  is  so  vague  that  two  points  of  contact  are  not  distinguished 
until  they  are  21  in.  apart.  It  is  found  that  the  points  of  the  com- 
passes must  be  more  widely  separated  when  the  test  is  made  in  the 
long  axis  of  a  limb  than  when  across  it.  (The  table  is  from  Kirke's 
Handhooh)  : 

Table  of  Variations  in  the  Tactile  Sensibility  of  Different  Parts. — 
(The  measurement  indicates  the  least  distance  at  which  the 
two  blunted  points  of  a  pair  of  compasses  could  be  separately 
distinguished. — E.  H.  Weber.) 

Tip  of  tongue ^-^  inch. 

Palmar  surface  of  third  phalanx  of  forefinger     .    .  xV 

Palmar  surface  of  second  phalanges  of  fingers     .    .  \ 

Red  surface  of  under  lip \ 

Tip  of  the  nose \ 

Middle  of  dorsum  of  tongue \ 

Palm  of  hand -f^ 

Centre  of  hard  palate \ 

Dorsal  surface  of  first  phalanges  of  fingers  ....  -^^ 

Back  of  hand 1^ 

Dorsum  of  foot  near  toes \\ 

Gluteal  region IJ 

Sacral  region 1\ 

Upper  and  lower  parts  of  forearm 1^ 

Back  of  neck  near  occiput 2 

Upper  dorsal  and  mid-lumbar  regions 2 

Middle  part  of  forearm 2\ 

Middle  of  thigh  _ 2\ 

Mid-cervical  region 2\ 

Mid-dorsal  region 2|^ 


How  is  touch  modified  by  education? 

The  sense  of  touch  may  be  greatly  educated  and  specialized. 
This  is  seen  in  many  of  the  arts  where  great  dexterity  obtains  by 
reason  of  an  educated  touch.  The  reading  raised  letters  by  the 
blind  is  a  familiar  example  of  educated  touch. 


TOUCH.  149 

What  is  pressure  sensation? 

Wlii-n  weight  is  atkled  to  an  ordinary  touch,  the  sensation  of  the 
pressure  of  the  weight  is  felt,  and  by  it  one  can  judge  with  con- 
siderable accuracy  the  amount  of  the  pressui'e,  and  determine  the 
comparative  pressure  of  two  weights  with  approximate  correct- 
ness within  limits  of  pressure.  This  is  known  as  the  sense  of 
pressure. 

What  is  the  muscular  sense? 

Ey  taking  a  body  in  the  hand  and  raising  it  we  feel  a  sense  of 
resistance  in  the  muscles,  by  whose  intensity  we  can  much  more 
accurately  determine  the  weight.  This  is  the  muscular  sense.  It 
is  developed  to  an  exceedingly  fine  degree  in  some  occupations ; 
for  example,  postal  clerks  detect  overweight  letters  with  wonderful 
accuracy  and  quickness. 

What  is  the  origin  of  the  muscular  sense  ? 

It  has  been  urged  that  the  muscular  sense  is  of  central  origin, 
and  depends  upon  the  strength  of  the  impetus  which  must  be 
sent  to  the  muscles  to  cause  them  to  do  certain  work.  It  may, 
however,  be  due  to  a  training  of  the  sensibility  of  the  muscle, 
whereby  the  relative  strength  of  a  contraction  is  perceived  as  a 
sensation. 

What  is  temperature  sense? 

The  surface  of  the  body  is  very  sensible  of  temperature  changes  ; 
and  that  this  is  distinct  from  ordinary  tactile  sensation  has  been 
inferred  from  the  fact  that  when  the  ordinary  touch  is  blunted  the 
temperature  sense  may  remain  unimpaired. 

Are  the  sensations  of  temperature  accurate  from  a  thermometric 
standpoint  ? 

No.  They  are  relative  ;  that  is,  we  infer  from  the  temperiiture 
of  the  skin  or  of  our  habitual  surroundings  the  warmth  or  coldness 
of  the  thing  tested.  It  is  related  that  Arctic  explorers  have  found 
the  water  feel  warm  when  swimming  in  pools  on  icebergs,  and  a 
drop  of  the  mercury  to  80°  F.  is  said  to  feel  cold  in  torrid  climates. 
A  more  simple  illustration  is  that  of  immersing  one  hand  in  water 
at  40°  F.  and  the  other  in  water  at  120°  F.,  and  then  both  in  water 
at  80°  F.,  when  one  hand  will  feel  hot  and  the  other  cold,  though 
both  are  subjected  to  the  same  temperature.  Again,  during  a  chill 
the  temperature  of  the  body  is  often  very  considerably  elevated, 
and  yet  the  sensation  is  entirely  of  cold. 


150  THE   SENSES. 

May  the  temperature  sense  be  educated  ? 

Yes.  For  example,  a  skilled  bath-attendant  is  able  to  determine 
with  an  astonishing  accuracy  the  temperature  of  water  by  immers- 
ing his  hand. 

Does  the  delicacy  of  the  temperature  sense  correspond  with  that 
of  touch  proper  ? 

Yes,  in  the  main,  but  there  are  some  situations  in  which  the 
skin  is  very  thin,  and  the  temperature  sense  is  relatively  much 
more  delicate  than  the  tactile. 

TASTE. 
What  conditions  are  necessary  for  the  sense  of  taste  ? 

Aside  from  the  conditions  which  are  always  necessary  for  sense- 
perception — viz.  proper  organs  for  receiving,  communicating,  and 
perceiving  the  sensory  impulse — there  must  be  present  a  sapid  sub- 
stance which  must  be  in  solution.  The  solution  in  the  case  of  dry 
substances  is  effected  by  the  saliva.  It  is  also  necessary  that  the 
surface  of  the  organs  of  taste  shall  be  moist. 

Where  does  the  sense  of  taste  arise  ? 

Chiefly  from  the  tongue,  though  there  is  some  power  to  taste 
resident  in  the  soft  palate,  fauces,  tonsils,  and  pharynx.  In  the 
tongue  the  taste  is  more  acutely  developed  in  the  posterior  portion, 
though  in  most  the  tip  and  sides  are  sensitive  to  taste.  The  cen- 
tral portion  of  the  dorsum  is  not  an  actively  sensitive  taste-organ. 
The  under  surface  of  the  tongue  is  little  if  at  all  sensitive  to  taste. 

What  nervous  supply  conducts  the  taste-sense  ? 

Probably  the  glosso-pharyngeal.  The  lingual  branch  of  the 
fifth  (or  gustatory)  is  also  a  conductor  of  taste-impressions  for 
the  front  of  the  tongue. 

Describe,  roughly,  the  tongue. 

The  tongue  is  a  flattened  muscular  organ  covered  by  epithelium. 
It  is  controlled  by  intrinsic  and  extrinsic  muscles,  which  give  it  a 
remarkable  flexibility  of  movement ;  the  latter  for  its  larger,  and 
the  former  for  its  more  delicate,  actions. 

What  kinds  of  papillae  characterize  the  mucous  membrane  of  the 
tongue  ? 
There  are  three  varieties  found,  which  are  known  as  filiform^ 
fungiform,  and  circumvallate  papillae.     These  are  set  chiefly  upon 


TASTE. 


151 


the  dorsum  of  the  tongue,  and  over  its  whole  surface  are  numer- 
ous mucous  follicles,  whose  secretions  keep  the  tongue  moist 
(Fig.  41). 

Fig.  41. 


A/. 

Upper  Surface  of  the  Tongue. 

Describe  the  filiform  papillae  of  the  tongue. 

The  filiform  papUhr.  are  set  mostly  upon  the  middle  of  the 
dorsum,  but  are  scattered  over  the  entire  surface,  and  are  far  more 
numerous  than  any  other  kind.  They  are  conical  in  shape,  and 
are  covered  with  epithelium,  which  projects  in  a  brush-like  tuft 
from  the  apex.  Their  function  is  mostly  tactile,  and  in  animals, 
especially  of  the  cat  tribe,  arc  very  prominent. 


152  THE   SENSES. 

Describe  the  fungiform  papillae. 

They  are  chiefly  distributed  over  the  sides  and  tip  of  the  organ, 
and  sparsely  upon  the  dorsum.  They  are  larger  at  the  surface 
than  at  the  base,  club-shaped,  and  are  supplied  with  blood-vessels 
and  nerves.     Their  funx5tion  is  probably  sensory. 

Describe  the  circumvallate  papillae. 

They  are  somewhat  similar  in  shape  to  the  fungiform,  but  con- 
siderably larger.  They  are  situated  at  the  posterior  portion  of  the 
dorsum  in  a  V-shaped  arrangement,  and  number  only  eight  or  ten. 
In  the  circumvallate  papillse  are  the  taste-goblets,  or  gustatory  buds, 
which  are  the  form  of  nerve-ending  characterizing  the  parts  where 
this  sense  is  developed. 

What  other  functions  are  dependent  upon  the  tongue  besides 
taste  ? 
The  sense  of  touch  is  very  highly  developed  here,  and  with  it 
the  sense  of  temperature,  pressure,  pain,  etc. :  upon  these  touch 
and  muscular  senses  to  a  great  extent  depend  the  accuracy  of  the 
tongue  in  many  of  its  important  uses — speech,  mastication,  deglu- 
tition, sucking.  The  tactile  sense  is  very  important,  too,  in  the 
sense  of  taste,  for  with  many  substances  the  taste  is  largely  due 
to  their  mechanical  condition :  this  is  the  case  with  mucilaginous, 
oily,  and  chalky  tastes. 

What  relation  has  the  sense  of  smell  to  taste  ? 

It  is  important,  for  with  many  substances — particularly  aromatic 
substances — of  food  and  drink  the  association  of  smell  and  taste  is 
very  essential  to  a  thorough  appreciation  of  a  flavor.  Most  cooked 
foods  lose  their  savor  if  the  nose  is  obstructed  ;  thus  with  a  "  cold" 
in  the  nose  "  everything  tastes  alike." 

What  kinds  of  flavors  are  appreciated  by  the  tongue  ? 

The  principal  tastes  are  sweet,  bitter,  acid,  alkaline,  and  saline. 
Besides  these,  the  general  sensibility  of  the  tongue  detects  pungent 
or  caustic  and  styptic  tastes,  as  well  as  the  oily  and  mucilaginous 
tastes. 

What  degree  of  taste-sensibility  has  the  tongue  ? 

It  is  quite  acute.  A  solution  of  acid  or  bitter  substances  is  tasted 
when  very  dilute :  strychnine  is  said  to  be  tasted  in  a  1  :  600,000 
solution ;  sulphuric  acid,  1  ;  1000. 


SMELL.  1 53 

Wliat  is  after-taste? 

After  an  aromatic  substance  has  been  tasted  there  remains  in  the 
mouth  an  impression  of  that  flavor,  and  if  such  substances  be  taken 
in  rapid  succession,  the  appreciation  of  their  flavor  is  lost.  This 
impression,  which  is  left  by  a  strong  flavorris  called  the  after-taste, 
and  is  utilized  sometimes  to  cover  the  taste  of  a  disagreeable  medi- 
cine, a  strongly-flavored  aromatic  preceding  it. 

Wiat  influence  upon  taste  has  the  muscular  action  of  the 
tongue  ? 
Twofcild.  It  breaks  the  food  up  more  thoroughly  by  its  pressure 
against  the  walls  of  the  mouth,  and  so  brings  it  into  a  better  con- 
dition to  reach  the  nerve-endings  ;  and  it  carries  the  food  about  the 
mouth,  so  that  the  taste-organs  are  able  to  reach  it  readily. 

SMELL. 
What  are  the  conditions  necessary  to  the  sense  of  smell? 

The  special  organs  for  this  sense  for  the  reception,  conduction, 
and  perception  of  the  stimulus,  as  in  the  case  of  any  of  the  senses, 
must  be  in  their  proper  condition,  and  a  stimulus  (an  odor;  must 
be  present  to  excite  them. 

What  are  odors  ? 

They  are  caused  either  by  minute  particles  of  solid  matter  or  by 
gases  which  are  in  the  atmosphere,  and  they  must  be  capable  of 
sohition  in  the  mucus  of  the  Schneiderian  membrane.  The  sub- 
stance must  pass  in  a  current  of  air  through  the  nostrils  or  it  is  not 
perceived  as  an  odor.  This  is  accomplished  by  "  sniffing  "  the  air, 
and  thus  creating  an  intermitting  current  which  is  tested  by  the 
olfactory  sense.  In  this  way  a  trace  of  a  gas  or  impalpable  powder 
may  be  detected  which  cannot  be  traced  by  chemical  or  other  means. 
If  the  substance  be  applied  as  a  solution,  it  is  not  detected ;  thus, 
rose-water  in  a  nasal  douche  is  not  noticed  while  the  nostrils  are 
full  of  fluid,  and  yet  as  soon  as  the  nostrils  are  free  the  odor 
appears. 

Where  is  the  organ  of  the  sense  of  smell  ? 

In  tlie  mucous  membrane  of  the  upper  part  of  the  nasal  cavity. 
The  olfactorj-  nerves  are  the  functional  nerves  of  the  sense,  and  are 
spread  out  in  a  fine  network  (Fig.  42)  over  the  surface  of  the  supe- 
rior or  turbinated  bone  and  upper  portion  of  the  middle  turbinated 
bone,  and  on  the  upper  third  of  the  septum.     The  nerves  end  in 


154 


THE   SENSES. 
Fig.  42. 


Distribution  of  Nerves  in  the  Nasal  Passages :  1,  olfactory  bulb,  with  its  nerves ;  2,  nasal 
branch  of  the  fifth  pair ;  3,  spheno-palatine  ganglion. 

special  end-organs,  known  as  olfactory  cells,  whicli  lie  under  tlie 
ciliated  epithelium  of  the  part. 

Describe  the  origin  of  the  olfactory  nerves. 

The  nerves  arise  from  a  mass  of  gray  matter  lying  beneath  the 
anterior  lobe  of  the  brain  upon  the  cribriform  plate  of  the  ethmoid 
bone.  This  is  the  olfactory  bulb,  and  it  is  connected  by  the 
olfactory  tract  with  the  cerebrum. 

Is  tactile  sensibility  a  property  of  the  olfactory  nerve  ? 

No.  The  lining  membrane  of  the  nasal  cavity  is  very  sensitive 
to  irritation,  but  the  nasal  branch  of  the  fifth  nerve  and  branches 
from  the  spheno-palatine  ganglion  furnish  the  ordinary  and  tactile 
sense. 

Do  the  perceptions  by  the  olfactory  and  by  the  nerves  of  touch 
resemble  each  other? 

Often  they  do,  and  some  stimuli  aifect  both  nerves.  The  com- 
mon sensibility  is  evoked  by  such  substances  as  are  irritating  and 
acrid  :  ammonia  gas  has  no  odor,  but  it  stimulates  the  mucous  mem- 
brane by  its  irritating  properties.  The  tactile  or  common  sensibil- 
ities remain  when  the  olfactory  are  gone.     The  relation  between 


HEARING.  155 

<lio  two  kinds  of  porcoption  is  lost  to  us,  and  we  speak  of  the  smell 
of  ammonia  or  of  aleoliol  when  it  is  probably  not  an  olfactory,  but 
a  sensory,  perception. 

Is  the  sense  of  smell  very  acute  ? 

Vi's,  but  not  so  sharp  in  man  as  in  many  of  the  lower  animals. 
Tlu"  distribution  of  the  olfactory  nerves  is  much  wider  in  some  of 
the  animals,  and  the  cerebral  development  is  correspondingly  in- 
creased. In  man  the  range  of  susceptibility  is,  however,  probably 
greater.  The  variety  of  odors  and  the  very  minute  quantity  of 
stimulant  substance  required  to  produce  a  sensation  of  smell  are 
quite  wonderful.  The  most  delicate  analysis  may  fail  to  show 
traces  of  the  substances  which  can  be  appreciated  by  the  sense  of 
smell. 

Is  the  same  odor  agreeable  to  all  men? 

No.  There  are  some  odors  pleasant  to  some  which  others  find  al- 
most intolerable.  Musk,  for  example,  is  a  pleasant  perfume  to  some, 
while  to  others  it  is  quite  unendurable.  In  the  same  way,  the 
acuteness  of  this  sense  in  some  is  more  marked  than  in  others,  and 
yet  this  may  apply  only  to  certain  kinds  of  odors. 

Is  sneezing  a  reflex  from  the  olfactory  nerve? 

Xo.      It  is  excited  through  the  fifth. 

Are  hallucinations  of  smell  common  ? 

They  often  occur,  and  in  cases  of  disease  of  the  olfactory  centres 
there  is  often  complaint  of  a  constant  bad  smell.  With  normal 
organs  there  may  be  a  sensation  of  an  odor  which  cannot  be  de- 
tected by  others  present. 

HEARINa. 
How  does  the  auditory  or  eighth  cranial  nerve  originate? 

The  fibres  arise  from  a  nucleus  of  gray  matter  in  the  floor  of  the 
fourth  ventricle,  and  from  this  source  pass  out  through  the  sub- 
stance of  the  medulla  in  a  number  of  small  bundles  which  unite 
with  another  root  from  the  crrchdJinn  to  form  a  trunk.  This  passes 
with  the  facial  nerve  into  the  internal  auditory  canal,  and  terminates 
in  special  end-organs  in  the  internal  ear. 

Describe,  roughly,  the  auditory  apparatus. 

It  consists  of  (1)  the  external  ear;  (2)  the  middle  ear;  and  (3) 
the  internal  ear. 


156  THE   SENSES. 

What  is  the  function  of  the  external  ear  ? 

It  serves  to  receive  tlie  sound-waves  and  to  indicate  the  direction 
from  which  they  come  in  animals  who  possess  the  power  of  moving 
the  organ.  Through  the  external  auditory  canal  the  sound-waves 
are  conducted  to  the  middle  ear. 

Describe  the  middle  ear. 

It  is  a  cavity  in  the  temporal  bone  which  is  shut  off  from  the 
external  auditory  canal  by  the  tympanum.  The  Eustachian  tube 
connects  this  cavity  with  the  pharynx.  The  lining  of  the  middle 
ear  is  ciliated  epithelium,  continued  from  the  mucous  membrane  of 
the  pharynx  through  the  Eustachian  tube.  There  are  two  openings 
of  importance — the  fenestra  rotunda  and  the  fenestra  ovalis — in  the 
bony  wall,  but  they  are  covered,  the  former  by  membrane,  the  latter 
by  the  stapes.  There  is  a  chain  of  small  bones  (ossicles)  which 
connect  the  tympanum  and  the  fenestra  ovalis. 

What  is  the  tympanum? 

It  is  a  tough,  tense,  fibrous  membrane  set  in  the  bony  opening 
of  the  external  auditory  canal.  The  degree  of  tension  of  the  tym- 
panum is  regulated  by  the  tensor  tympani  muscle. 

Fig.  43. 


Right  Temporal  Bone  of  the  New-born  Infant,  seen  from  its  inner  side,  showing  the  mem- 
brana  tympani  and  chain  of  bones  in  their  natural  position  (Rudinger). 

What  is  the  function  of  the  ossicles  ? 

They  are  three  in  number,  and  are  so  articulated  as  to  commu- 


HEARING. 


157 


nicate  the  vibration  of  the  tvinpuiiuiii  to  the  internal  car  (Fipj.  48). 
The  liaiulle  of"  the  maUeus  is  attached  to  the  tynipaiuuu,  so  that 
this  bone  moves  with  each  vi))ration.  This  motion  is  communi- 
cated to  the  incus,  whidi  passes  it  on  to  the  stapes.  The  stapes 
I'nrms  a  sort  of  ])istoii  in  tlie  foramen  ovalis,  and  is  therefore  capa- 
ble of  transmitting  to  the  fluid  in  the  cavity  of  the  labyrinth  the 
impulses  which  it  receives. 

Describe  the  arrangement  of  the  internal  ear. 

The  internal  ear,  or  labyrinth,  is  situated  in  the  dense  petrous 
portion  of  the  temporal  bone,  and  consists  of  three  essential  parts : 
the  vestibule  (Fig.  44),  and  opening 
from  it  the  semicircular  canals  and  the 
cochlea.  There  is  another  opening, 
the  jequeductus  vestibuli,  whose  use 
is  unknown,  and  still  others  for  the  en- 
trance of  the  auditory  nerve-filaments. 
Within  the  bony  structure  is  a  mem- 
brane of  fibrous  and  epithelial  tissue, 
the  membranous  labyrinth,  which  fol- 
lows the  bony  structure  and  contains 
a  colorless  fluid,  the  endolymjjh,  and  a 
fluid  stirrounds  this  membranous  laby- 
rinth, the  perilymph. 

What  is  the  fiinction  of  the  semicir- 
cular canals? 
These  canals  are  arched  cylindrical 
spaces  in  the  solid  bone  which  open  at 
each  end  of  the  arch  in  the  vestibule. 
They  are  three  in  number,  and  two 
are  nearly  vertical  and  one  is  horizontal 
in  such  a  manner  that  the  planes  of  the  two  vertical  canals  are  at 
right  angles,  one  being  fore  and  aft,  and  the  other  transverse  (Fig. 
44).  Their  use  does  not  seem  to  be  directly  connected  with  the 
auditory  function  of  the  part,  but  to  be  connected  more  with  the 
sense  of  equilibrium.  The  movement  of  the  fltiids  in  the  canals, 
arranged  in  the  directions  of  the  three  dimensions,  may  serve  to 
produce  sensations  which  lead  to  the  formation  of  accurate  judg- 
ment of  changes  in  the  position  of  the  body. 

What  is  the  cochlea? 

It  is  a  part  of  the  labyrinth  which  derives  its  name  from  its 


External  View  of  a  fast  of  the  Left 
Labj-riuth  (Heiile) :  /,  fenestra 
cochleie,  or  round  window ;  a, 
fenestra  vestibuli,  or  oval  win- 
dow ;  6,  ampulla  of  superior  semi- 
circular canal ;  d,  common  shaft 
of  union  of  these  two  canals;  e, 
ampulla  of  the  horizontal  semi- 
circular canal ;  g,  tractus  spiralis 
foraniinosus. 

These  canals  are  arranged 


158 


THE  SENSES. 


resemblance  to  a  snail-shell.  It  is  divided  into  two  parts,  by  bony 
and  membranous  structures,  which  run  parallel  from  base  to  apex 
of  the  spiral  (Fig.  45).     The  upper  passage  opens  into  the  vesti- 

FiG.  45. 


Bony  Cochlea  of  the  Human  Ear,  right  side,  opened  from  its  anterior  face  (Cruveilhier). 

bule,  and  is  known  as  the  scala  vestibuli ;  the  lower,  the  scala 
tympani,  is  shut  oif  by  a  membranous  partition,  which  covers  the 
foramen  rotundum.  from  the  cavity  of  the  tympanum.  The  scala 
vestibuli  is  subdivided  by  a  fibrous  membrane  (of  Reissner)  which 
passes  from  the  bony  lamina  spiralis  to  the  wall  of  the  scala  ves- 
tibuli, shutting  off  a  triangular  space  (canalis  cochlearis).  The 
floor  of  this  space  is  the  membranous  partition  (membrana  basi- 
laris)  which  separates  the  scala  tympani  from  it,  and  upon  this 
membrane  is  the  organ  of  Corti. 

What  is  the  function  of  the  cochlea  ? 

It  is  to  spread  out,  over  as  large  a  surface  as  may  be,  the  mech- 
anism for  the  reception  of  sounds  by  the  organ  of  Corti,  the  end- 
organ  of  the  auditory  nerve.  It  seems  to  be  especially  well  adapted 
for  this  purpose,  because  the  solid  spiral  lamina  connects  it  with  the 
bony  framework  of  the  skull,  while  it  is  contained  in  the  mem- 
branous labyrinth,  whose  fluid  contents  fit  it  for  the  response  to 
vibrations.  It  is  further  insulated  by  its  suspension  in  the  peri- 
lymph. These  peculiarities  favor  the  conduction  of  semi-vibra- 
tions through  the  bone,  as  well  as  of  vibrations  through  the 
mechanism  of  the  middle  ear. 


HEARING.  159 

Describe  the  organ  of  Corti. 

l']i(iii    (he    hasihir   iiu'iiiliraiic  is   arranged   ;i  S(!rlcs   of  rafter-like 
bodies  which  roof  in  ;i  small  canal  (Fig.  40)  :   upon  this  are  spread 

Fig.  46. 


t 


I'iagrainalic  Sfi'tiou  of  the  Org;in  of  Corti:  1,  iiieiubrana  basilaris ;  2,  3,  internal  aud 
exlorual  libres  of  the  arch;  4,  eiiitheliuiii  cells  uear  its  inner  and  outer  borders; 
5,  Hair-cells  lying  in  contact  with  the  arch  (magnified  500  diameters). 

the  functional  nerve-endings  of  the  auditory  nerve.  They  are 
large  nucleated  cells,  the  rods  of  Corti,  having  hair-like  processes 
which  project  into  the  canalis  cochlearis  or  scala  media.  When 
looked  at  from  above  the  cells  have  an  appearance  similar  to  the 
keyboard  of  a  piano.  Fibres  of  the  auditory  nerve  spread  to  these 
cells  from  the  bony  lamina  spiralis. 

What  peculiarity  of  structure  of  the  auditory  nerve  is  noteworthy  ? 
Its  hbres  are  non-medullated,  and  it  contains  numerous  ganglion- 
cells.  In  the  cochlea  there  are  many  of  these  cells,  and  they  form 
plexuses  of  nerve-fibres  to  supply  the  hair-cells.  The  absence  of 
neurilemma  in  the  auditory  nerve  gives  it  a  soft  feel  which  has 
caused  the  name  "  portio  mollis  "  to  be  given  to  it  when  it  and  the 
facial  are  considered  as  a  single  nerve. 

What  is  the  physiological  action  of  the  organ  of  Corti  ? 

It  is  probable  that  each  of  the  functitnial  cells  in  the  organ  of 
Corti  responds  to  a  particular  shade  of  sound.  How  this  occurs  is 
not  understood,  but  the  vibrations  of  the  tympanum  arc  communi- 
cated to  the  stapes  by  the  other  ossicles  ;  and  these  cells  seem  to  be 
able  to  respond  each  to  a  particular  tone  by  its  sensitiveness  in 
selecting  its  particular  rate  of  vibration. 

What  is  the  musical  range  of  human  hearing  ? 

About  seven  octaves.  There  are  about  three  thousand  hair-cells 
in  the  organ  of  Corti,  and  it  will  be  easily  seen  that  this  would 
allow  an  enormous  capability  to  differentiate  sounds  and  musical 
tones. 


160  THE  SENSES. 

What  subjective  sensations  of  hearing  occur  ? 

They  may  be  due  to  disturbances  of  the  auditory  apparatus  or 
to  abnormal  conditions  of  surrounding  organs.  Thus,  buzzing  or 
ringing  in  the  ears  may  result  from  the  hypersemia  of  the  parts 
and  exaggerated  rush  of  blood,  or  from  a  defect  in  the  circulating 
apparatus  (as  by  an  aneurism),  or  from  disease  in  the  auditory 
nerve  or  some  other  portion  of  the  apparatus.  Hallucinations  of 
hearing  are  very  common  among  the  insane. 

How  is  the  voice  produced? 

The  vibration  of  the  vocal  cords  is  produced  by  the  passage  of 
the  air  in  expiration,  never  naturally  in  inspiration.  The  quality 
of  the  voice  as  regards  pitch  depends  upon  the  length  of  the  vocal 
cords,  the  crieo-thyroid  muscles  acting  to  increase  the  tension, 
vrhile  the  thyro-arytenoid  relax  the  cords  and  the  crico-arytenoids 
dilate  and  contract  the  rima  glottidis.  Falsetto  and  high-pitched 
notes  in  a  naturally  low-pitched  voice  are  due  to  vibration  at  the 
edges  of  the  cords.  The  hollow  spaces  about  the  oral  and  nasal 
cavities  are  of  use  as  resonators  or  sounding-boards. 

What  organs  are  used  in  the  formation  of  articulate  speech  ? 

The  tongue  and  teeth  in  the  formation  of  the  Unguals  and  den- 
tals, the  nasal  sounds  by  the  cavity  of  the  nose ;  the  other  sounds 
are  formed  largely  by  modifications  in  the  shape  of  the  mouth  in 
one  or  another  part. 

What  range  has  the  human  voice  in  respect  of  pitch  ? 

From  one  to  three  octaves :  in  this  cultivation  and  natural  apti- 
tude are  factors  which  permit  great  variability.  The  total  range 
of  the  human  voice  from  the  highest  soprano  to  the  lowest  bass  is 
about  four  octaves.  Thus  it  will  be  seen  that  the  range  of  sounds 
which  can  be  appreciated  by  the  ear  is  far  beyond  the  capacity  of 
the  voice. 

SIG-HT. 

What  is  the  function  of  the  eye  ? 

The  reception  of  stimuli  of  light,  whereby  we  are  able  to  per- 
ceive the  impressions  of  form,  color,  and  conditions  of  our  sur- 
roundings in  infinite  variety.  It  is  far  the  most  complex  in 
structure  of  any  of  the  organs  of  special  sense,  and  the  most  rapid 
and  delicate  in  its  actions. 


SIGHT.  161 

What  is  the  origin  of  the  optic  or  second  cranial  nerve  ? 

It  arises  l»y  two  roots — oiiu  in  the  corpora  (|uadrigeiiiiiia,  and  the 
other  in  the  optic  thahimus — with  many  fibres  derived  from  centres 
of  vision  in  the  posterior  portion  of  the  cerebral  lobes.  These 
fibres  unite  and  form  a  nerve-trunk  (the  optic  tract)  which  en- 
circles the  crus  cerebri,  meeting  the  tract  of  the  opposide  side  just 
in  front  of  the  pituitary  body.  Here  there  is  a  fusion  of  the  two 
optic  tracts  in  a  partial  decussation,  some  fibres  going  to  the  eye 
of  the  same  side,  and  some  decussating.  The  fibres  then  pass  to 
each  eye  as  the  optic  nerve,  which  is  distributed  by  special  nerve- 
endings  in  the  retina. 

Has  the  optic  nerve  any  other  physiological  property  than  that  of 
conduction  of  special-sense  impulses  ? 
No.     Tt  has  no   common   sensibility.     It  is,  however,  the  con- 
ductor of  afferent  impulses  for  the  iris  reflex. 

What  is  the  effect  of  stimulation  of  the  divided  optic  nerve  ? 

None,  for  the  peripheral  end  ;  for  the  central  portion,  a  sensation 
of  light  and  contraction  of  the  pupil. 

What  accessory  apparatus  is  important  to  the  protection  of  the 
eye? 
Eyelids  and  lachrymal  gland. 

Describe  the  eyelids. 

Each  eye  has  two  lids,  an  upper  and  lower.  Each  consists  of  a 
thin  plate  of  elastic  tissue  with  a  covering  of  loose  skin  and  a 
smooth  lining  of  mucous  membrane — the  conjunctiva — which  is 
reflected  upon  the  eyeball.  Along  the  edges  of  the  lids  are  a 
number  of  short  curved  hairs  which  screen  the  eye  from  foreign 
bodies.  The  extreme  sensitiveness  of  the  conjunctiva  helps  in 
this  by  giving  immediate  warning  when  any  foreign  substance 
gets  in  the  eye. 

What  is  the  lachrymal  gland? 

Tt  is  a  small  racemose  gland  lodged  in  the  upper  and  outer  part 
of  the  orbit.  It  has  several  ducts,  which  lead  to  the  surface  of 
the  conjunctiva  of  the  upper  lid.  The  secretion  of  the  gland  is 
usually  just  sufficient  to  keep  the  eye  moist,  but  under  the  stimu- 
lus of  pain  or  intense  emotion  the  secretion  is  increased,  and  ap- 
pears in  drops  which  flow  from  the  eyes — tears.  Under  ordinary 
circumstances  a  slight  excess  of  this  moisture  is  drained  into  the 

11— Phy. 


162 


THE   SENSES. 


nasal  cavity  by  the  lachrymal  duct.  This  secretion  is  slightly 
alkaline,  and  contains  about  1  per  cent,  of  solids,  chiefly  sodium 
chloride. 

What  are  the  Meibomian  glands  ? 

They  are  a  number  of  small  racemose  glands,  lying  beneath  the 
conjunctiva,  which  secrete  an  oily  protective  substance.  The  ducts 
of  these  glands  open  along  the  edge  of  the  lid. 

Describe  the  eyeball. 

It  consists  of  a  tough,  opaque  globe  (Fig.  47),  having  a  some- 

FiG.  47. 


Horizontal  Section  of  the  Eight  Eyeball:  1,  optic  nerve;  2,  sclerotic  coat;  3,  cornea; 
4,  canal  of  Schlemm ;  .5,  choroid  coat;  6,  ciliary  muscle;  7,  iris;  8,  crystalline  lens; 
9,  retina;  10,  hyaloid  membrane;  11,  canal  of  Petit;  12,  vitreous  body. 


what  more  sharply-curved  translucent  portion,  the  cornea,  at  the 
front.  It  has  in  the  anterior  portion  a  lens^  and  in  front  and 
behind  this  are  chambers  which  contain  fluids :  the  one  in  front  is 


SIGHT. 


163 


[■ 


the  anterior  chnmher,  and  contains  the  aqueous  fluid,  while  the 
posterior  is  the  vifreotts  /iiniinr.  These  structures  fill  the  eyeball 
and  give  it  a  tense  feel  to  the  touch. 

What  are  the  coats  of  the  eyeball  ? 

(1)  Tlu!  .«/iiii.  or  sc/<r"fic  eodt,  is  external,  and  covers  about 
live-sixths  of  the  globe.  The  cornea  is  continuous  with  it  in  front. 
It  is  composed  of  tough  white  fibres  arranged  in  interconinumi- 
catiug  layers.  (2)  The  choroid  coat  is  very  vascular,  being  com- 
posed of  a  mesh  of  capillaries.  There 
is  outside  of  this  a  layer  of  connective  Fig.  48. 

tissue  containing  pigment-granules. 
(3)  The  retina,  which  is  the  seat  of 
the  end-organs  of  the  optic  nerve. 

Describe  the  retina. 

It  consists  of  the  nervous  mechanism 
of  the  eye  lying  in  a  loose  connective 
tissue,  and  beneath  it  n  2'>igment-Iayer. 
Without  entering  into  the  details  of 
its  numerous  layers,  we  may  say  that 
the  fibres  of  the  optic  nerve  spread 
out,  divested  of  neurilemma,  in  this 
membrane,  and  communicate  with 
ganglion-cells,  which  are  abundant. 
The  fibres  pass  inward  and  terminate 
in  the  layer  of  rods  and  cones  which 
form  the  end-organs  of  the  nerve. 

Describe  the  rods  and  cones  of  the 
retina. 

They  are  closely  packed  at  the  sur- 
face of  the  retina,  the  rods  being  the 
more  numeroiis  in  most  situations. 
The    cones  seem  to  be  modifications  ,.  ^v^   - 

of  the  rods,  and  their  office  is  essen-  SfCt^Jn'^^^f^^s^ 
tially  similar.  The  rods  (Fig.  48)  are 
straight  cylindrical  bodies  of  a  trans- 
parent substance,  and  are  placed  par- 
allel to  one  another  and  perpendicular 
to  the  surface  of  the  eyeball.  In  length  they  are  about  five  to  seven 
times  the  diameter  of  a  red  blood-corpuscle,  and  in  diameter  about 


Diagrammatic  Section  from  the  pos- 
terior Portion  of  the  Human  Ret- 
ina: 1,  layer  of  rods  and  cones; 
2,  layer  of"  nuclei  (Schultze). 


164  THE  SENSES. 

one-twentieth  of  their  length.  The  cones  are  very  similar,  except 
that  their  conical  shape  makes  them  appear  to  be  of  different  cha- 
racter. The  cones  do  not  always  reach  to  the  same  level  as  the 
rods.  When  viewed  from  the  retinal  surface,  the  ends  of  the  rods 
and  cones  give  the  appearance  of  a  fine  mosaic.  These  organs  are 
connected  with  the  subjacent  nervous  tissue,  but  the  mode  of  their 
connection  with  the  optic  nerve  is  not  fully  understood. 

Considered  as  an  apparatus,  how  is  the  eye  arranged? 

It  may  be  compared  to  the  photographic  camera.  It  contains  vari- 
ous media  for  the  refraction  of  light,  and  a  screen  at  the  back  for 
receiving  the  image.  The  refracting  media  are  the  cornea,  aqueous 
humor,  crystalline  lens,  and  the  vitreous  humor :  the  screen  is  the 
retina.  The  pigment  of  the  retina  and  choroid  makes  the  interior 
dark,  a  necessary  feature  in  such  an  apparatus.  The  mechanism  of 
the  lens  enables  the  eye  to  be  focused  for  distance,  while  the  iris 
regulates  the  proper  admission  of  light. 

What  is  the  structure  of  the  cornea  ? 

It  is  continuous  with  the  sclera  in  the  front  of  the  eye,  and 
occupies  about  one-sixth  of  the  surface  (3,  Fig.  47).  Its  shape  is 
that  of  a  small  dome  set  upon  the  globe  of  the  eye.  It  has  in 
front  several  layers  of  epithelial  cells,  and  at  the  posterior  surface 
a  thin  epithelial  lining  (membrane  of  Descemet)  ;  but  the  main 
body  of  the  structure  consists  of  interlacing  connective-tissue  fibres, 
which  have  spaces  in  which  are  found  branching  cells  peculiar 
to  the  structure.  The  cornea  is  perfectly  transparent :  it  has  no 
blood-vessels. 

Describe  the  crystalline  lens. 

It  is  a  double  convex  lens  (8,  Fig.  47)  of  high  refractive  power 
which  is  suspended  in  the  anterior  portion  of  the  eye  immediately 
behind  the  anterior  chamber.  Its  function  is  to  bring  the  rays  of 
light  to  a  focus  upon  the  retina.  In  structure  the  lens  is  com- 
posed of  concentric  layers  of  long,  slender  fibres  enclosed  in  a  thin 
capsule. 

What  are  the  aqueous  and  vitreous  humors  ? 

(1)  The  aqueous  humor  is  a  watery  fluid  contained  in  the 
anterior  chamber.  It  acts  with  the  cornea  as  a  refracting  medium 
to  concentrate  rays  of  light  upon  the  lens,  to  maintain  the  globular 
form  of  the  cornea,  and  to  float  the  iris  and  allow  it  freedom  of 
motion. 


SIGHT.  165 

(2)  The  vitreous  body  (or  humor)  is  a  semifluid  gelatinous 
substance  which  fills  the  posterior  chamber  and  constitutes  about 
four-fifths  of  the  bulk  of  the  eye.  It  is  quite  transparent,  and 
acts  to  maintain  the  tension  of  the  eyeball,  and  as  a  refracting 
medium  through  which  the  light  reaches  the  retina. 

What  is  the  pupil? 

The  pupil  is  the  aperture  through  which  light  enters  the  dark 
chamber  of  the  eye.     It  is  a  circular  opening  in  the  iris. 

What  is  the  iris? 

It  is  a  curtain  of  muscular  tissue  placed  vertically  in  front  of 
the  lens.  The  fibres  of  the  muscular  tissue  are  both  circular  and 
radiating,  so  that  they  serve  to  decrease  and  increase  the  size  of 
the  pupil  as  one  or  the  other  set  of  fibres  acts.  It  has  a  pigment- 
layer  upon  the  inner  surface,  which  is  continued  from  the  choroid, 
and  upon  the  amount  of  the  coloring-matter  depends  the  "  color  of 
the  eyes." 

What  nervous  action  controls  the  ciliary  muscles? 

Contraction  or  dilatation  of  the  pupil  is  a  reflex  act,  and  the 
afferent  stimulus  is  carried  through  the  optic  nerve  and  the  motor 
through  the  third  cranial  nerve,  acting  from  a  centre  just  beneath  the 
aqueduct  of  Sylvius  and  the  corpora  quadrigemina.  The  increase 
in  the  amount  of  light  which  reaches  the  retina  causes  a  contrac- 
tion of  the  pupil,  and  a  decrease  is  followed  by  dilatation.  Aside 
from  this,  the  needs  of  the  eye  regulate  the  amount  of  light ;  thus, 
for  near  work  the  pupil  contracts,  and  dilates  when  the  eye  is 
focused  upon  a  distant  object. 

What  other  influences  control  the  iris? 

The  pupil  is  controlled  also  through  the  sympathetic,  and  the 
fifth  nerve  through  the  connection  of  the  third  and  fifth  nerves 
with  the  ciliary  ganglion  of  the  sympathetic  system.  Drugs  are 
active  also,  both  locally  and  internally,  in  controlling  the  action  of 
the  iris  without  reference  to  the  reflex  fibres :  atropine  both  locally 
and  internally  dilates  the  pupil ;  opium  internally,  and  eserine  locally 
contract  it. 

What  is  accommodation  in  vision? 

The  eye  is  able  to  see  objects  close  at  hand  and  at  a  distance 
with  equal  clearness,  though  perhaps  not  with  equal  regard  for  the 


166  THE  SENSES. 

minuter  details.  This  is  known  as  tlie  accommodation  of  the  eye. 
In  optical  instruments  this  j)rocess  of  accommodating  the  instru- 
ment to  the  focal  distance  is  called  focusing.  So  is  accommodation 
an  automatic  focusing  of  the  eye. 

How  is  accommodation  effected? 

By  the  ciliary  muscle.  The  crystalline  lens  is  suspended  in  its 
capsule  by  the  suspensory  ligament,  and  this  is  controlled  by  the 
ciliary  muscle.  At  rest  the  eye  is  focused  for  seeing  at  a  distance, 
and  the  lens  is  held  somewhat  flattened  by  the  tension  of  the  sus- 
pensory ligament.  When  focusing  upon  a  near  object  the  ciliary 
muscle  contracts,  and  the  lens  is  permitted  to  project  more  as  the 
tension  of  the  ligament  relaxes. 

What  is  the  near-point? 

It  is  the  nearest  point  to  the  eye  at  which  vision  is  distinct,  the 
shortest  focus  of  the  crystalline  lens.  It  is  usually  about  5  or  6 
inches. 

What  is  an  emmetropic  eye  ? 

It  is  the  normal  eye  ;  that  is,  an  eye  in  which  parallel  rays  or 
rays  from  objects  at  a  distance  are  focused  upon  the  retina  without 
an  effort  at  accommodation.  Such  a  distance,  for  practical  pur- 
poses, is  considered  to  be  any  point  beyond  20  feet.  Absolutely 
emmetropic  eyes  are  not  common. 

What  is  myopia  ? 

Near-sight.  In  this  case  the  rays  from  a  distance  are  focused  in 
front  of  the  retina,  and  the  image  is  blurred.  Such  an  eye  is  per- 
manently focused  for  near  objects. 

How  is  myopia  produced? 

In  two  ways,  by  the  antero-posterior  diameter  of  the  eye  being 
too  great,  or  by  the  convexity  of  the  lens  being  exaggerated.  In 
either  case  the  focus  of  the  lens  will  fall  in  front  of  the  retina. 

How  is  myopia  corrected? 

By  the  use  of  a  concave  lens  which  diverges  the  rays,  and  in  this 
way  prevents  their  coming  to  a  focus  too  soon.  Such  glasses  are 
seldom  needed  except  for  distant  vision. 

What  is  hypermetropia  ? 

Far-sight.     In  this  case  the  lens  focuses  behind  the  retina  iia 


SIGHT.  167 

near   vision,  and   the  image   is   blurred   as   in  myopia  for  distant 
vision. 

What  are  the  causes  of  hypermetropia  ? 

Shortening  of  the  antero-pusterior  axis  of  the  eye  or  abnormal 
flattening  of  the  lens,  Avliich  does  not  allow  accommodation  for  near 
vision. 

How  is  hypermetropia  corrected  ? 

By  the  use  of  convex  lenses,  which  add  to  the  refractive  power 
of  the  eye. 

What  is  astigmatism? 

A  defect  in  the  vision  due  to  the  irregularity  in  the  globe  of  the 
eye,  whereby  the  diameter  in  one  plane  is  greater  than  in  another. 
Thus,  the  retina  may  be  an  uneven  surface,  and  the  image  focus 
accurately  in  one  part  and  falsely  in  another.  In  this  condition 
vertical  and  horizontal  lines  are  not  seen  with  equal  distinctness. 

How  is  astigmatism  corrected? 

By  the  use  of  cylindrical  or  prismatic  glasses,  which  have  to  be 
accurately  adapted  to  the  needs  of  each  case.  This  error,  if  seri- 
ous, is  usually  combined  with  other  defects  of  vision,  frequently 
myopia. 

What  is  presbyopia? 

Defective  vision  due  to  the  loss  of  power  in  advanced  years.  The 
elasticity  of  the  lens  becomes  less,  and  the  convexity  cannot  be  in- 
creased for  near  vision.  The  ciliaiy  muscle  may  also  be  weaker 
and  aid  in  the  production  of  the  error.  A  weak  convex  glass  com- 
monly corrects  the  lack  of  refraction-power. 

Is  the  eye  achromatic? 

Yes.  It  may,  however,  be  said  that  there  may  be  a  visible  band 
of  color  seen  by  some  defective  eyes  where  there  is  considerable 
fault  in  the  focus  of  the  image  on  the  retina. 

What  is  the  "  blind  spot "  ? 

The  point  of  entrance  of  the  optic  nerve  is  not  sensitive  to  light, 
and  at  this  point  an  image  thrown  upon  the  retina  is  not  seen  ; 
therefore  it  is  called  the  blind  spot. 

How  is  the  blind  spot  demonstrated? 

If  the  left  eye  is  covered  and  the  right  directed  steadily  upon 


168  THE  SENSES. 

the  cross  in  Fig.  49,  the  circular  spot  will  be  visible  at  the  same 
time,  though  less  distinctly.  As  the  book  is  moved  slowly  back- 
ward and  forward,  a  point  will  be  found  at  which  the  round  spot 

Fig.  49. 


disappears,  reappearing  as  the  book  is  held  nearer  or  farther  or  as 
it  is  inclined  in  either  direction  and  the  image  is  carried  away  from 
the  blind  spot. 

What  part  of  the  retina  possesses  the  most  acute  vision  ? 

The  portion  directly  behind  the  lens,  where  the  mi.cula  lutea  (yel- 
low spot)  with  its  central  depression  (fovea  centralis)  is  situated. 
Here  are  found  none  of  the  fibres  of  the  optic  nerve,  but  a  great 
increase  in  the  number  of  the  cones  of  the  layer  of  rods  and  cones, 
as  well  as  an  increase  in  their  size.  In  looking  at  any  object  it  is 
upon  this  spot  that  its  image  is  reflected  by  the  media,  and  here 
the  power  of  the  end-organs  of  the  optic  nerve  is  most  highly 
developed. 

What  conclusion  is  drawn  from  these  facts  ? 

That  the  rods  and  cones  (more  especially  the  cones)  are  the 
physiological  agents  for  the  reception  of  light  stimuli :  for  upon  the 
blind  spot  is  no  layer  of  the  rods  and  cones,  while  in  the  point  of 
sharpest  sight  the  nerve-fibres  are  wanting,  and  these  elements  are 
especially  prominent. 

What  is  the  duration  of  visual  sensations  ? 

The  duration  of  a  visual  sensation  is  always  greater  than  that 
of  the  stimulus  which  has  caused  it.  However  brief  the  luminous 
impression,  the  effect  on  the  retina  lasts  about  one-eighth  of  a  sec- 
ond. The  spokes  of  a  rapidly-revolving  wheel  for  this  reason  do 
not  appear  as  spokes,  but  as  a  solid  mass,  each  following  one 
another  so  rapidly  that  one  impression  cannot  fade  before  another 
has  replaced  it. 


SIGHT.  169 

What  is  the  retinal  red? 

When  tlio  retina  (»f  a  recently-killed  animal  is  examined  it  is 
colorless,  but  during  life  or  if  extracted  without  exposure  to  light, 
it  is  of  a  purple-red  hue,  and  the  color  is  found  in  the  rods  of  the 
retina.  It  is  derived  iVom  the  pigment  of  the  deeper  part  of  the 
retina.  It  is  the  "■  retinal  red  "  or  '•  visual  purple,"  as  it  is  variously 
named,  which  one  sees  in  the  reflex  of  the  retina. 

What  effect  has  exposure  to  light  upon  the  retinal  red? 

It  destroys  it,  and  for  this  reason  it  was  long  unknown.  It  dis- 
appears after  a  brief  exposure  to  sunlight,  about  half  a  minute. 

How  may  the  retinal  red  be  seen? 

By  throwing  a  beam  of  light  into  the  eye  by  a  mirror,  as  by  the 
ophthalmoscope,  a  red  glow  is  observed  in  the  pupil.  This  is  called 
the  retinal  reflex. 

What  are  optograms? 

Pictures  which  appear  upon  the  retina  after  exposure  to  light. 
They  are  due  to  the  fact  that  an  exposure  to  light  bleaches  the 
retinal  red,  leaving  it  dark  in  the  shaded  portions. 

How  are  optograms  obtained? 

The  eye  is  removed  from  an  animal  in  a  dark  room  and  kept  in 
a  covered  box  until  exposed  to  a  brightly  illuminated  skylight  or 
window  for  some  minutes.  The  eye  is  then  replaced  in  the  dark 
room  and  the  retina  examined.  It  will  be  found  that  the  panes  of 
the  window  are  shown  in  light  color,  while  the  sash  is  in  dark  out- 
line. This  soon  fades  on  exposure  to  daylight,  but  if  the  retina  is 
dried  in  the  dark  the  optogram  is  much  more  durable. 

Is  the  pigment  of  the  retina  essential  to  vision  ? 

iNo,  but  it  is  of  considerable  use  in  rendering  the  eyeball  a  dark 
box.  which  is  of  importance  here  as  in  all  optical  instruments. 

How  is  the  real  image  formed  by  a  double  convex  lens? 

It  is  an  inverted  imago  at  the  point  of  focus  of  the  lens  if  the 
luminous  object  is  placed  at  a  distance  (Fig.  50).  Referring  to 
this  figure,  it  will  be  seen  that  the  rays  originating  at  A  will  be 
twice  refracted,  once  by  the  lens  and  again  in  leaving  it,  so  that  all 
rays  from  A  reaching  the  lens  are  joined  at  a.  The  same  is  true  for 
B  and  h.  Therefore  a  screen  placed  at  the  focus,  F,  will  receive  an 
inverted  image,  a  b,  of  the  luminous  object,^V  B. 


170 


THE   SENSES. 
Fig.  50. 


Formation  of  Image  by  Convex  Lens. 

Does  the  crystalline  lens  throw  an  inverted  image  upon  the 
retina  ? 
Yes.     This  may  easily  be  demonstrated  by  looking  at  the  image 
from  behind  a  fresh  eye  of  an  albino  animal  (white  rabbit)  or  if 
the  sclera  be  thinned. 

How  is  this  inversion  corrected? 

The  correction  is  made  by  the  brain  in  its  perception  of  the  image. 
It  is  an  act  of  mental  and  not  of  physical  origin.  Thus,  objects 
which  are  projected  upon  the  left  of  the  retinal  surface  look  to  be, 
as  they  are,  on  the  right  of  the  body  ;  and  so  with  all  the  direc- 
tions :  the  inversion  of  the  retinal  image  is  corrected  by  the  mind. 

What  other  visual  perceptions  are  the  result  of  mental  processes  ? 

We  are  able  to  estimate  by  the  aid  of  the  brain  the  size,  direc- 
tion, distance,  form,  and  speed  of  motion  of  a  thing  which  we  have 
seen.  All  of  these  are  judgments  based  largely  upon  previous 
experience.  All  of  these  deductions  are  liable  to  error  by  reason 
of  faulty  judgiuent  or  faulty  vision,  but  this  is  the  usual  method 
of  forming  such  estimates. 

How  does  the  eye  perceive  colors  ? 

It  is  probable  that  particular  rods  and  cones  are  capable  of  re- 
sponding to  rays  of  light  of  a  certain  wave-length,  and  to  those  rays 
alone.  It  is  well  known  that  the  rays  of  red  light  are  of  a  certain 
length  of  vibration.  The  same  is  true  of  yellow  and  of  green  rays. 
We  can  conceive  that  each  primary  color  has  its  own  set  of  cones 
and  rods  capable  of  responding  to  its  stimulus,  and  that  by  combi- 
nations of  these  stimuli  the  complementary  colors  and  variations  of 
shade  may  be  perceived  by  the  resulting  stimuli  acting  upon  the 
brain-centres.  Such  teaching  is,  of  course,  speculative,  but  this  is 
one  theory  which  has  acceptance. 


SIGHT.  171 

What  is  color-blindness? 

All  iiialiility  tu  perueivc  some  colors.  The  colors  which  are 
usually  mistaken  are  green  and  red.  Frequently  it  is  found  that 
a  distinction  cannot  be  made  between  these  colors.  This  is  some- 
times known  as  Daltonism. 

What  is  the  cause  of  color-blindness  ? 

It  is  probably  due  to  the  absence  of  the  rods  and  cones  which 
are  capable  of  responding  to  the  stimulus  of  rays  of  a  certain  wave- 
length. 

Is  this  an  important  defect? 

Yes.  In  marine  and  land  locomotion  red  and  green  signals  are 
used  to  indicate  opposite  conditions,  and  the  failure  to  distinguish 
them  has  freciuently  been  the  cause  of  serious  accidents. 

How  is  color-blindness  tested? 

By  laying  a  number  of  skeins  of  yarn  of  various  colors  in  a 
heap,  and  requiring  the  person  to  be  tested  to  select  all  resembling 
a  certain  skein  from  the  hea}). 

Do  the  eyes  act  both  at  once,  or  do  we  see  with  one  at  a  time  ? 

AVe  use  both  m  ordinary  vision  at  the  same  time. 

What  is  diplopia? 

It  is  the  condition  which  results  from  a  want  of  harmony  in  the 
eyes,  so  that  the  image  of  each  eye  is  perceived  separately  ;  that 
is,  one  sees  double. 

What  are  the  common  causes  of  diplopia  ? 

Paralysis  or  spasm  in  one  of  the  lateral  straight  muscles,  which 
does  not  allow  the  eye  to  be  turned  in  harmony  with  the  other. 
If  the  eyes  are  turned  so  that  the  axes  of  vision  are  separated,  the 
condition  is  known  as  external  strabismus  or  squint  ;  if  the  axes 
are  crossed,  it  is  called  internal  strabismus  or  cross-eye. 

What  benefits  result  from  binocular  vision? 

'{'he  ideas  of  form  and  distance  are  much  more  correctly  judged 
liy  the  perceptive  fiiculties.  This  is  due  to  the  fact  that  the  object 
viewed  is  seen  beyond  its  equator,  so  to  speak,  by  each  eye.  and 
the  combined  image  is  therefore  less  flat  in  appearance  than  in 
monocular  vision. 


172  THE  SENSES. 

What  instrument  is  devised  to  take  advantage  of  this  ? 

The  stereoscope.  In  this  instrument  two  photographs  are  taken 
hy  cameras  so  placed  as  to  represent  the  position  of  the  eyes  in 
vision,  and  the  two  views  of  one  object  are  then  superimposed  by 
the  use  of  prisms. 

What  determines  the  clearness  of  vision  ? 

The  space  between  the  cones  in  the  point  of  clearest  vision,  the 
macula  lutea.  It  has  been  calculated  that  an  object  must  sub- 
tend an  arc  of  at  least  60  to  70  seconds  in  the  field  of  vision  to  be 
clearly  seen.  Such  an  object  makes  an  image  of  about  -12-5^^-0*  of 
an  inch  in  the  retina ;  and  this  is  about  the  distance  between  the 
cones  at  the  macula  lutea.  Similarly,  two  points  to  be  clearly 
distinguished  must  be  separated  sufficiently  to  allow  this  amount 
of  separation  in  the  retinal  image. 

What  are  after-images? 

It  has  already  been  noted  that  vision  lasts  longer  than  the 
stimulus  which  excites  it.  Under  some  conditions  it  may  last 
a  perceptibly  long  time :  it  is  then  known  as  an  after-image. 
If  one  looks  at  an  intense  light,  the  sun,  the  sense  of  light  remains 
for  some  time  in  the  eye.  Similarly,  if  one  looks  intently  at  a 
white  spot  on  a  black  background,  and  then  turns  to  a  white 
surface,  one  has  the  image  of  a  gray  spot.  The  first  of  these 
conditions  cited  is  known  as  a  positive  after-image,  and  the  latter 
as  a  negative.  In  the  first  case  the  phenomenon  results  in  a  con- 
tinuation of  the  same  sensation,  and  in  the  latter  a  new  perception 
results. 

What  peculiarity  do  the  after-images  of  colored  objects  present  ? 

They  appear  to  have  the  complementary  color  of  the  original 
object;  thus,  green  excites  a  reddish  after-image;  orange,  blue; 
and  so  on. 

How  are  after-images  explained? 

They  may  be  explained  as  a  result  of  exhaustion.  The  part  of  the 
retina  on  which  the  image  has  fallen  becomes  tired,  and  when  the 
eye  is  turned  upon  a  white  ground,  the  white  light  coming  to  the 
retina  does  not  produce  as  much  sensation  in  the  tired  portion. 
The  colored  negative  after-images  may  be  similarly  explained. 

*  Variously  estimated  at  12^ 00  to  ^oVo  of  an  inch. 


EMBRYOLOGY.  173 

EMBRYOLOGY. 

REPRODUCTION. 
What  is  a  species? 

It  is  a  class  of  organized  beings  in  which  the  individuals 
composing  it  die  ott",  but  which  nevertheless  repeats  itself  and 
maintains  its  complement  by  the  continued  accession  of  similar 
forms. 

What  is  reproduction? 

It  is  the  process  by  which  a  species  is  perpetuated,  notwith- 
standing the  limited  existence  of  the  individual  members. 

What  law  governs  the  reproduction  of  species  ? 

The  young  are  of  the  same  kind  as  their  parents.  By  this  law, 
which  is  so  commonly  observed  as  to  seem  a  truism,  is  maintained 
the  anatomical  identity  of  individuals  of  a  species,  as  well  as  the 
physiological  fact  of  an  unbroken  continuance  of  the  species  by 
reproduction. 

What  is  sexual  generation? 

It  is  reproduction  of  a  species  by  a  union  of  elements  produced 
separately  by  the  female  and  the  male.  The  female  produces  the 
ovum,  or  egg,  which  is  capable  of  being  developed  into  a  living 
offspring  only  when  it  is  fecundated  or  impregnated  by  the  seminal 
or  spermatic  element  from  the  male. 

What  are  the  organs  of  generation  of  the  female  ? 

They  consist  of  two  ovaries,  in  which  the  ova  are  formed,  and 
their  oviducts  or  Fallopian  tnhes,  which  carry  the  ova  to  the  womb, 
in  which  they  may  develop  if  fecundated  by  the  male ;  and  the 
vagina  for  the  reception  of  the  male  organ  in  copulation  and  for 
the  subsequent  discharge  of  the  foetus  (Fig.  51). 

Describes  the  ovaries. 

They  are  two  organs  lying  one  on  each  side  of  the  uterus,  in  the 
folds  of  the  broad  ligament.  In  size  they  are  about  l-l  in.  long,  1 
in.  wide,  and  •]  in.  in  thickness.  Besides  lying  between  the  layers 
of  the  broad  ligament,  they  are  stayed  in  their  position  by  an  at- 
tachment to  the  fundus  of  the  uterus  and  to  the  fimbriated  extrem- 
ity of  the  Fallopian  tube. 


174 


EMBRYOLOGY. 


What  is  the  minute  structure  of  an  ovary  ? 

It  may  be  described  as  a  ductless  gland  in  which  the  component 
elements  are  (1)  a  stroma  of  connective  tissue  and  unstriped  mus- 


Generative  Organs  of  the  Human  Female :  «,  a,  ovaries ;  6,  6,  Fallopian  tubes ;  c,  body  of 
the  uterus ;  d,  cervix  ;  e,  vagina. 

cle-cells,  and  with  them  a  great  number  of  peculiar  spindle-shaped 
branching  cells ;  and  (2)  the  glandular  portion,  characterized  by 
the  Graafian  follicles. 

What  are  the  Graafian  follicles? 

They  are  best  observed  during  the  childbearing  age.  They  lie 
in  the  periphery,  and  present  various  appearances  as  they  are  more 
or  less  matured.  Some  are  large  enough  to  be  seen  by  the  unaided 
eye,  while  others  are  very  minute.  In  the  matured  follicle  the  in- 
terstitial tissue  will  be  found  to  have  collected  in  a  wall,  quite  well 
defined,  which  is  lined  by  an  epithelial  layer ;  and  upon  one  side 
this  epithelium  is  heaped  up  into  a  mass,  the  germ-Mil  (cumulus 
proligerus),  which  contains  the  ovum.  The  remainder  of  the  fol- 
licle is  filled  with  a  colorless  fluid. 

How  does  the  ovum  leave  the  ovary  ? 

As  the  Graafian  follicles  mature,  they  approach,  and  often  pro- 


REPRODUCTION. 


175 


Fig.  52. 


ject  above,  the  surface  of  tlie  ovary.     The  fluid  contcnt.s  of  the 
follit'Ie  increases  and   the  wall   jjecoiues 
thinner  over  it,  until    finally    it    bursts, 
and   the    ovum   with    some   of  its   sur- 
rounding epithelium  escapes. 

What  peculiarity  of  the  ovary  favors 
the  escape  of  the  ovum? 
Tlie  ovary  is  covered  with  a  thin 
layer  of  epithelium  (^tlie  germinal  epi- 
fhcluini),  and  not  by  the  serous  mem- 
brane which  lines  the  abdominal  sur- 
f\ices  of  the  rest  of  the  viscera.  This 
is  of  great  importance  in  the  life  of 
the  ovum,  for  it  renders  it  possible  for 
it  to  enter  the  orifice  of  the  Fallopian 
tube  without  interfering  with  the  peri- 
toneum and  without  having  to  pass  so 
dense  a  structure.  . 

Fig.  53. 


Human  Ovum,  rui)fured  by 
Pressure,  showing  tlie  vitellus 
partially  expelled,  the  gernii- 
native  vesicle,  with  its  germi- 
uative  spot,  at  a,  and  the 
smooth  fracture  of  the  vitel- 
line membrane. 


Section  of  the  Ovary  (after  Schron) :  1,  outer  covering;  1',  attached  border;  2,  central 
stroma;  3,  peripheral  stroma;  4,  blood-vessels  ;  5,  Graafian  follicles  in  their  earliest 
sta^e  ;  6,  7,  8,  more  advanced  follicles  ;  !),  an  almost  mature  follicle  ;  9',  follicle  from 
which  the  ovum  has  esciped  ;  10,  corpus  luteum. 

Whence  is  the  ovum  derived? 

It  is  a  very  highly  developed  cell,  wliich  is  derived  from  the 
germinal  epithelium  covering  the  ovary.  In  the  development  of 
the  ovary  this  epithelium  dips  into  the  surface  of  the  organ,  and  a 


176 


EMBRYOLOGY. 


certain  portion  is  finally  walled  off  by  growth  of  the  surface  cells. 
Thus  a  ball  of  epithelial  cells  is  introduced  into  the  body  of  the 
organ,  and  one  cell  develops  the  ovum,  the  rest  going  on  to  make 
up  the  Graafian  follicle  and  the  trerm-hill.  (See  5,  6,  7,  8,  9, 
Fig.  53.) 

Describe  the  ovum. 

It  is  a  minute  globular  cell  containing  a  nucleus  and  nucleolus. 
In  diameter  it  is  a  little  less  than  y^g  in.  (Fig.  54). 

Fig.  54. 


Semi-diagrammatic  Representation  of  a  Mammalian  Ovum,  highly  magnified :  sp,  zona 
pellucida;  vi,  vitellus  ;  gv,  germinal  vesiale;  ffs,  germinal  spot. 

What  is  the  zona  pellucida  or  vitelline  membrane? 

It  is  a  thick  hyaline  membrane  (cell-wall)  which  encloses  the 
cell. 

What  is  the  vitellus  ? 

It  is  a  granular  protoplasm  which  makes  up  the  cell-body. 

What  is  the  germinal  vesicle  ? 

It  is  the  nucleus  of  the  cell  ;  a  somewhat  large,  transparent,  and 
well-defined  body  set  somewhat  eccentrically  in  the  vitellus — the 
yolk  of  the  egg. 

What  is  the  germinative  spot  ? 

The  nucleolus  of  the  cell.     In  addition  to  the  nearly  transparent 


REPRODUCTION.  177 

fluid  which   the  nucleus  contains,  there  is  a  small  dark,  almost 
opaque  spot,  the  germinal  spot  of  the  ovum. 

Do  all  the  Graafian  follicles  develop  ova? 

No.  From  puberty  to  the  menopause  the  formation  of  new 
Graafian  follicles  is  continuous,  and  a  very  great  number  are  pro- 
duced, but  many  do  not  develop  ova,  and  so  waste  away  without 
going  through  the  changes  described. 

Describe  the  Fallopian  tubes. 

These  tubes  ai-e  about  82  inches  in  length,  and  extend  from  the 
fundus  of  the  uterus  laterally  on  each  side.  The  calibre  of  the 
tubes  gradually  narrows  from  without  inward,  until  at  the  uterus 
the  opening  is  very  minute.  The  external  covering  is  peritoneum, 
but  the  lining  is  of  mucous  membrane,  having  ciliated  epithelium. 
The  outer  end  of  the  Fallopian  tube  is  free  and  fringed — the  fimbri- 
ated extremity. 

What  is  the  function  of  the  fimbriated  end  of  the  Fallopian 
tube? 

To  grasp  the  ovary  during  sexual  excitement  and  prevent  the 
escape  of  an  ovum  which  may  extrude — the  "  morsus  diaboli." 

What  is  the  use  of  the  ciliated  epithelium  ? 

To  carry  the  ovum  to  the  uterus.  This  is  also  accomplished  by 
the  action  of  the  circular  and  longitudinal  muscular  fibres. 

Describe  the  uterus. 

It  is  a  somewhat  pear-shaped  organ,  and  is  about  3  in.  in  length, 
its  wider  part  being  about  2  in.  wide  and  the  cervix  1  in.  It  is 
described  as  consisting  of  a  fundus,  body,  and  cervix.  The  body 
unites  the  fundus  with  the  cervix,  which  extends  into  the  vagina. 

What  structures  compose  the  uterus? 

It  is  covered  over  nearly  all  of  its  external  surface  by  (1)  peri- 
toneum. Its  bulk  is  made  up  of  unstriped  (2)  muscle,  which  oc- 
curs in  longitudnal  and  circular  bundles  and  layers.  This  muscu- 
lar tissue  increa.ses  enormously  during  pregnancy,  and  by  its 
strength  helps  to  extrude  the  foetus.  Tlie  lining  is  of  (3)  mucous 
mcralirane,  which  is  formed  in  its  superficial  layer  of  ciliated 
columnar  epithelium.  In  the  mucous  membrane  of  the  cervix  are 
a  number  of  follicles  which  secrete  a  viscid,  tenacious  mucus,  by 
which  the  os  uteri  is  frequently  found  to  be  plugged. 
12— Phy. 


178  EMBRYOLOGY. 

Describe  the  vagina. 

It  is  a  membranous  canal  about  5  in.  long,  extending  from  the 
uterus  to  the  external  genitals.  It  is  lined  with  mucous  mem- 
brane, which  in  the  ordinary  contracted  state  is  thrown  into  folds, 
its  anterior  and  posterior  walls  being  in  contact.  There  is  consider- 
able erectile  tissue  in  the  mucous  membrane.  At  the  orifice  of  the 
vagina  externally  is  a  sphincter  which  only  partially  contracts  it, 
and  besides  this  there  are  longitudinal  and  transverse  unstriped 
muscle-fibres  in  the  submucous  tissue.  The  outlet  of  the  vagina 
is  sometimes  also  partially  closed  in  the  virgin  by  the  hymen,  a 
fold  of  mucous  membrane. 

What  are  the  external  organs  of  generation  ? 

The  external  organs  of  generation  are  not  immediately  connected 
with  the  function  of  reproduction,  and  may  be  enumerated  as  the 
labia  majora  and  minora,  clitoris,  and  the  meatus  urinarius. 

What  are  the  organs  of  generation  in  the  male  ? 

The  two  testicles  which  produce  the  seminal  fluid,  and  the  vas 
deferens;  or  duct  leading  from  each  to  the  seminal  vesicles,  where 
the  secretion  is  stored  until  it  is  discharged  through  the  penis. 

What  is  the  structure  of  the  testicles  ? 

Each  testicle  is  made  up  of  a  dense  connective-tissue  framework 
and  a  secreting  portion.  The  connective-tissue  stroma,  tunica  albu- 
ginea,  surrounds  the  outside  of  the  organ,  and  sends  incomplete 
partitions  into  the  central  portion  of  the  organ,  dividing  it  into  a 
number  of  communicating  cavities.  In  these  cavities  are  winding 
tubules  which  constitute  the  secreting  portion  of  the  organ.  These 
tubules  inosculate  in  a  sort  of  mesh  (reti  testis),  and  finally  all 
unite  in  the  epididymis.  The  secreting  tubules  are  called  the 
seminiferous  tubules. 

How  do  the  seminiferous  tubules  secrete  the  spermatic  fluid? 

Each  tubule  has,  in  the  active  organ,  a  limiting  membrane,  upon 
which  are  a  number  of  layers  of  flattened  cells.  Internal  to  these 
are  seminal  cells  in  two  or  more  layers.  The  seminal  cells  contain 
nuclei  which  are  capable  of  division,  so  that  each  nucleus  may  de- 
velop several  new  nuclei.  The  nuclei  are  the  spermatoblasts,  or  cells 
from  which  the  spennatzoa  originate.  The  cells  before  the  division 
of  the  nuclei  resemble  the  oi'dinary  cuboid  epithelium,  and  it  is  in 
the  superficial  layers  (i.  e.  toward  the  lumen  of  the  tubuli)  that 
this  function  of  tlae  cells  takes  place. 


REPRODUCTIOlf. 


179 


Fig.  55. 


How  is  the  seminal  fluid  conveyed  from  the  testis? 

The  .SL-miiiiitjruu.s  tubules  all  cuiivergc  toward  the  epididymis, 
a  tortuous  tubule  which  is  lined  with  mucous  membrane,  and  lies 
beside  the  testis  in  a  long,  convoluted  mass  which  may  be  unrav- 
elled, and  is  found  to  be  about  20  feet  long.  This  empties  its  con- 
tents, or  rather  continues  on,  in  the  vas  deferens,  which  conveys  the 
somen  to  the  seminal  vesicles.  During  this  passage  the  mucous 
membrane  adds  a  viscid  mucous  secretion  in  which  the  spermato- 
zoa are  liberated  and,  so  to  speak,  diluted. 

What  is  the  appearance  of  the  spermatozoa  ? 

In  the  seminiferous  tubules  the  developing  spermatozoa  may  be 
seen  with  the  heads  all  united  in  the  cells  from  which  they  arise, 
the  tails  projecting  brush-like  into  the  cavity  of  the 
tube.  But  they  are  soon  separated.  Tliey  then  con- 
sist of  a  head  and  a  tail  (Fig.  55).  In  length  they 
are  about  ^^  to  ^ij;  of  an  inch.  The  head  is  some- 
what elliptical  and  the  tail  gradually  tapers.  In  other 
animals  than  man  the  size  and  form  vary  from  those 
of  man,  though  in  a  general  way  they  conform. 

What  action  of  the  spermatozoon  permits  it  to  enter 
the  uterus  and  Fallopian  tube  ? 
There  is  a  very  active  vibratory  motion  of  the  tail 
of  the  spermatozoon,  which  allows  it  quite  free  motion 
in  a  fluid  medium.  It  is  by  this  swimming  motion,  in 
which  it  may  be  compared  to  a  tadpole,  that  the  semi- 
nal cells  are  able  to  reach  the  ovum  against  the  action 
of  the  cilia  in  the  uterus  and  Fallopian  tube. 

Is  a  single  spermatozoon  sufficient  to  fecundate  an 
ovnm? 
It  probablvis.  There  have  been  more  than  one  seen 
in  an  impregnated  ovum,  but  it  is  probable  that  only 
one  enters  into  the  formation  of  the  male  pronucleus, 
the  rest  remainins  inactive. 


Human  Sper- 
niat  ozoon : 

1,  in  profile ; 

2,  viewed  on 
the  flat:  b, 
head :  c,  mid- 
dle-piece ;  <l, 
tail ;  e,  end- 
piece  of  the 
tail. 


Where  is  the  ovnm  impregnated  ? 
In  tile  Fallopian  tube. 

What  leads  us  to  the  conclusion  that  the  egg  is  fecundated  in 
the  Fallopian  tube? 
(1)  The  spermatozoa  are  found  there.     (2)  Before  the  ovum 


180  EMBRYOLOGY. 

leaves  the  Fallopian  tube  it  has  gained  an  albuminous  coat  which 
would  probably  be  impervious  to  the  spermatozoa.  (3)  The  unim- 
pregnated  egg  degenerates  before  it  enters  the  uterus,  and  is  then 
probably  incapable  of  impregnation. 

What  are  the  seminal  vesicles  ? 

They  are  tubules  which  join  the  vasa  deferentia,  and  lie  upon 
the  base  of  the  bladder,  emptying  into  the  urethra  by  the  ejacu- 
latory  ducts  through  the  prostate  gland.  In  structure  the  vesiculae 
seminales  are  convoluted.  They  are  lined  by  a  mucous  membrane 
which  is  convoluted  and  folded  so  as  to  give  it  a  sacculated 
appearance. 

What  is  the  prostate  gland  ? 

.  It  is  a  gland  lying  at  the  base  of  the  bladder  and  surrounding 
the  urethra  at  its  beginning.  It  has  the  general  structure  of  the 
glandular  organs,  and  in  addition  a  considerable  amount  of  muscu- 
lar tissue.  Its  acini  empty  into  ducts  which  empty  in  the  urethra. 
Its  function  is  not  exactly  known. 

Describe  the  penis. 

It  consists  of  three  more  or  less  cylindrical  bodies  of  erectile 
tissue  enclosed  in  fibrous  sheaths.  The  two  corpora  cavernosa  lie 
above,  and  receive  between  them,  below,  the  corpus  spongiosum,  in 
which  the  urethra  is  contained.  The  glans  penis  is  continuous 
with  the  corpus  spongiosum.  The  covering  of  the  penis  is  of 
loose  skin,  but  over  the  glans  penis  and  lining  the  prepuce  it 
resembles  mucous  membrane.  In  this  region  there  is  an  abundant 
subcutaneous  nerve-plexus,  and  the  Pacinian  bodies  are  quite 
numerous,  so  that  it  is  possessed  of  acute  sensibility. 

Describe  the  urethra. 

It  extends  from  the  bladder  through  the  corpus  spongiosum  to 
the  end  of  the  penis.  It  is  lined  with  mucous  membrane,  and  is 
furnished  in  its  deeper  layers  with  numerous  muscular  fibres. 
There  are  a  number  of  ducts  of  glands  opening  into  it  whose 
function  is  not  fully  understood,  though  their  secretion  is  sup- 
posed to  be  added  to  that  of  the  seminal  vesicles  to  make  up  the 
semen. 

How  is  the  erectile  tissue  of  the  penis  arranged  ? 

The  erectile  tissue  consists  of  a  system  of  distensible  veins  lying 
in   the   interstices  of  a  fibrous    connective   tissue.      The   erector 


REPRODUCTION.  181 

penis  muscle  by  its  contraction  compresses  the  veins  of  the  organ, 
and  the  veins  become  turgid  with  blood.  The  arteries  enter  the 
structure  of  the  erectile  tissue  along  the  pubic  bone,  and  are  not 

pressed  upon  by  the  contraction  of  the  muscle. 

What  is  menstruation? 

It  is  a  periodical  change  which  accompanies  ovulation  in  women. 

Is  menstruation  dependent  upon  the  ripening  and  discharge  of  an 
ovum? 

No.  The  phenomena  of  menstruation  may  occur  without  the 
rupture  of  a  Graafian  follicle,  and,  on  the  other  hand,  ovulation 
may  occur  in  amenorrhoeic  women.  As  a  rule,  however,  the  two 
processes  are  simultaneous,  and  the  discharge  of  an  ovum  occurs 
during  the  period. 

What  is  the  character  of  the  menstrual  discharge  ? 

It  is  a  thin,  bloody  fluid  of  a  dark  color  and  having  a  peculiar 
odor.  It  consists  of  blood,  epithelium,  and  mucus  from  the  uterus 
and  vagina,  together  with  the  decidua  menstrualis.  The  blood 
does  not  clot. 

What  is  the  decidua  menstrualis? 

It  is  a  membrane  developed  by  the  uterine  mucous  membrane 
for  the  purpose  of  furnishing  a  site  for  the  implantation  and  growth 
of  an  impregnated  ovum.  It  occurs  entirely  within  the  body  of 
the  organ,  and  does  not  extend  into  the  cervix.  If  impregnation 
does  not  occur,  the  decidua  menstrualis  breaks  down  and  leaves  its 
vessels  bleeding. 

Why  does  not  the  menstrual  blood  clot? 

Probably  because  of  its  mixture  with  the  mucus  of  the  uterus 
and  vagina. 

What  is  the  duration  of  menstrual  life  ? 

ITsually  in  temperate  climates  from  fourteen  or  fifteen  to  forty-five 
or  fifty  years  of  age.  The  periods  recur  regularly  at  intervals  of 
about  four  weeks,  but  the  occurrence  of  pregnancy  causes  a  cessa- 
tion which  lasts  through  lactation,  with  occasional  exceptions. 

What  is  the  corpus  luteum? 

After  the  escape  of  an  ovum  there  is  an  effusion  of  blood  into 
the  cavity  of  the  Graafian  follicle.  The  clot  which  follows  is  dis- 
posed of  by  the  same  retrogressive  processes  which  extravasated 


182 


EMBRYOLOGY. 


blood  may  undergo  in  any  part  of  the  body.  The  serum  is  absorbed, 
the  cells  disintegrate,  and  the  coloring  matter  is  in  part  taken  up 
by  the  tissues  and  in  part  crystallizes  or  takes  up  other  constitu- 
ents, and  presents  variations  of  coloring.  Hand  in  hand  with  these 
changes  in  the  blood  go  important  changes  in  the  surrounding 
tissues.  The  epithelial  cells  which  are  left  behind  proliferate  and 
form  a  soft  yellowish,  very  vascular  tissue,  which  presently  under- 
goes fatty  degeneration.  This  yellow  mass  surrounding  and  en- 
closing the  remains  of  the  extravasated  blood  constitutes  the  corpus 
luteum,  and  as  it  disappears  its  place  is  occupied  by  a  dense,  firm 
connective-tissue  cicatrix,  which  may  be  pigmented. 

How  does  the  corpus  luteum  behave  during  pregnancy? 

It  then  does  not  degenerate  and  disappear  rapidly  as  after  men- 
struation, but  continues  fully  as  large  for  several  months,  and  at 
the  end  of  pregnancy  still  remains  as  a  clearly  marked  body.  This 
is  shown  in  the  following  table  from  Dalton  : 


Corpus  Luteum  of  Menstrua- 
tion. 


Gor-pus  Luteum  of  Pregnancy 
(Dalton). 


At  the  end  of 

three  weeks. 

One  month. 


Two  months. 
Four  months. 

Six  months. 

Nine  months. 


f  in.  in  diameter;  central  clot  reddish;  convoluted  wall 
pale. 


Smaller ;  convoluted  wall 
bright  yellow ;  clot  still 
reddish. 

Reduced  to  the  condition  of 
an  insignificant  cicatrix. 

Absent  or  unnoticeable. 


Absent. 


Larger ;  convoluted  wall 
bright  yellow ;  clot  still 
reddish. 

I  in.  in  diameter ;  convo- 
luted wall  bright  yellow ; 
clot  perfectly  decolorized. 

Size  about  as  at  two  months ; 
clot  pale  and  fibrinous ; 
convoluted  wall  dull  yel- 
low. 

Still  as  large  as  at  the  end 
of  the  second  month.  Clot 
fibrinous.  Convoluted  wall 
paler. 

J  in.  in  diameter ;  central 
clot  converted  into  a  radi- 
ating cicatrix ;  external 
wall  tolerably  thick  and 
convoluted,  but  without 
any  bright  yellow  color. 

At  what  time  is  the  ovum  liable  to  impregnation? 

Probably  most  so  immediately  before  the  menstrual  period,  but 


Absent. 


DEVELOPMENT.  183 

owing  to  the  fact  that  both  the  female  and  male  elements  may 
remain  in  the  genital  passages  of  the  female  for  some  days  in  a 
healthy  condition,  it  is  difficult  tu  tix  the  time  of  actual  impreg- 
nation uf  the  ovum. 

What  facts  lead  to  the  supposition  that  impregnation  takes  place 
most  commonly  before  menstruation  ? 

(1)  It  is  )iiol)able  that  in  most  instances  the  rupture  of  the 
Graafian  follicle  occurs  very  early  in  the  menstrual  period.  (2) 
The  uterus  is  in  the  most  favorable  condition  to  sustain  the  fecund 
ovum  at  that  time,  because  of  the  presence  of  the  decidua  men- 
strualis.  (3)  Among  the  Jews,  a  remarkably  prolific  race,  coitus 
is  prohibited  by  the  religious  law  for  a  week  after  menstruation. 

DEVELOPMENT. 
What  changes  occur  in  the  ovum  before  impregnation? 

The  ovum,  after  leaving  the  ovary  and  while  still  in  the  Fallo- 
pian tube,  undergoes  certain  changes.  These  changes  are  mostly 
confined  to  the  nucleus  or  germinal  vesicle.  The  germinal  spot  or 
nucleolus  disappears,  and  the  outline  of  the  vesicle  becomes  indis- 
tinct, elongated  so  that  it  has  a  spindle-shape.  While  in  this  con- 
dition the  spindle  develops  two  or  three  vesicles,  which  collectively 
form  the  female  jjronucleus. 

Wkat  changes  in  the  ovum  follow  impregnation? 

The  head  of  a  spermatozoon  penetrates  the  vitelline  membrane 
and  enters  the  vitellus,  where  it  remains  surrounded  by  protoplasm. 
This  is  the  male  pronucleus.  The  male  and  female  pronuclei  soon 
join,  and  then  follows  a  process  of  growth  by  the  splitting  up  of 
the  nuclei  to  form  new  nucleated  protoplasmic  cells. 

What  is  this  splitting-up  process  called? 

.Segmentation.  The  first  cell  which  is  formed  by  the  union  of 
the  male  and  female  pronuclei  is  called  the  blastosphere  or  primi- 
tive segmentation   germ. 

What  other  change  then  occurs  ? 

The  ovum  receives  an  addition  of  a  layer  of  clear  albuminous 
material  while  still  in  the  Fallopian  tube,  which  adds  considerably 
to  its  bulk.     This  corresponds  to  the  white  of  a  hen's  egg. 

What  is  segmentation  of  the  vitellus  ? 

The  next  change  which  occurs  in  the  impregnated  egg  is  the  split- 


184  EMBRYOLOGY. 

ting  up  of  the  vitellus  or  yelk,  first  in  halves,  then  in  quarters,  and 
so  on  until  the  vitellus  becomes  a  mass  of  minute  granular-look- 
ing nucleated  cells  (Fig.  56).  The  segmentation  of  the  nucleus 
continues  with  the  corresponding  change  in  the  yelk. 

Fig.  56. 


Segmentation  of  the  Vitellus  in  the  Impregnated  Egg  of  the  Rabbit  (Coste). 

"Where  does  this  change  occur? 

In  the  Fallopian  tube.  The  human  ovum  probably  remains  in 
the  Fallopian  tube  for  eight  or  ten  days  before  reaching  the  uterus, 
and  while  there  does  not  materially  alter  its  appearance.  Barring 
the  fact  that  there  is  added  to  its  circumference  an  albuminous 
layer,  it  is  unchanged  in  external  looks. 

What  is  the  germinal  membrane? 

The  outer  layers  of  vitelline  cells  after  segmentation  are  closely 
packed  and  resemble  polygonal  epithelial  cells,  and  in  fact  form  a 
sort  of  lining  to  the  zona  pellucida,  holding  the  liquid  of  the  vitel- 
lus in  a  central  cavity.  This  lining  is  the  germinal  membrane  or 
blastoderm. 

Why  does  the  segmentation  of  the  vitellus  take  place  ? 

This  is  not  known,  nor  is  it  understood  how  it  occurs,  but  it  fol- 
lows the  union  of  the  male  and  female  elements  of  generation  only. 


DEVELOPMENT. 


185 


How  are  changes  in  the  developing  ovum  commonly  studied? 

la  the  devclupmont  ol'  the  of;g  of'  the  cuiniiioM  I'uwl.  I'his  is 
on  account  of  the  accuracy  with  whicli  the  time  of  development 
may  be  watched,  and  the  convenience  to  the  observer  of  such  sim- 
ple growth  by  incubation  compared  with  uterine  growth.  The  pro- 
cesses of  development  arc  not  materially  different. 

What  changes  occur  in  the  blastoderm? 

There  appears  at  one  point  an  opa<|uc  streak  (Fig.  57),  which  is 

Fig. 57. 


Diagram  of  the  Area  Germinativa,  showing  the  primitive  trace  and  area  pellucida. 


found  to  be  due  to  the  proliferation  of  the  cells  of  the  blastoderm. 
This  is  ih.Q  primitive  trace,  and  it  grows  in  length  and  breadth. 

What  changes  occur  in  the  arrangement  of  the  cells  of  the  blasto- 
derm at  this  time? 

They  separate  into  three  layers,  the  ejyihliut,  virsohhtst,  and  hi/po- 
hhisf  (Fig.  58)  ;  and  along  the  axis  of  the  primitive  trace  a  grot)ve 
is  formed  which  is  destined  to  become  the  cerebro-spinal  axis.  This 
is  the  primitive  groove. 

What  changes  occur  in  the  zona  pellucida  at  the  entrance  of  the 
ovum  into  the  uterus? 

The  surface  of  the  ovum  becomes  shaggy  with  tlie  appearance  of 


186 


EMBRYOLOGY. 


numerous  villi,  whicli  are  probably  derived  from  the  epiblast.     This 
is  known  now  as  the  chorion. 

What  changes  occur  in  the  uterus? 

The  decidua  menstrualis  has  been  mentioned  as  specially  suitable 
for  the  reception  of  the  ovum.  But  if  impregnation  occur,  it  is 
not  called  by  this  name,  as  menstruation  does  not  occur.  It  is 
then  known  as  the  decidua  vera.     It  consists  of  a  thick,  succulent 


Section  of  a  Blastoderm  at  right  angles  to  the  long  axis  of  the  embryo,  near  its  middle, 
after  eight  hours'  incubation  (from  Foster  and  Balfour) :  A,  epiblast  formed  of  two 
layers  of  cells ;  B,  mesoblast  thickened  below  the  primitive  groove ;  C,  hypoblast, 
formed  of  one  layer  of  flattened  cells;  pr,  primitive  groove;  mc,  mesoblast  cell; 
bd,  formative  cells  in  the  so-called  segmentation  or  subgerminal  cavity.  (The  line 
of  separation  between  the  epiblast  and  mesoblast  below  the  primitive  groove  is  too 
strongly  marked  in  the  figure.) 


mucous  membrane  caused  by  the  proliferation  of  the  subepithelial 
cells.  Into  this  decidua  the  ovum  falls,  and  its  shaggy  chorion 
implants  its  villi  in  the  crypts  of  the  mucous  membrane.  The 
decidua  soon  envelops  it,  and  the  portion  which  is  reflected  over 
the  ovum  is  known  as  the  decidua  reflexa. 

What  important  changes  now  begin  to  occur  in  the  blastoderm  ? 

The  blastoderm,  which  is  increasing  in  area  from  the  rapid  pro- 
liferation of  cells,  folds  at  each  end  transversely  and  at  the  sides 
longitudinally.  These  folds  are  of  great  importance,  for  it  is  in 
this  way  that  the  contour  of  the  body  is  outlined,  and  if  it  were 
not  for  them  the  blastoderm  would  continue  to  develop  as  a  flat 
surface.     The  transverse  folds  are  at  each  end,  and  are  known  as 


DEVELOPMENT.  187 

the  heiid  and  tall  folds.     Tlie  longitudinal  folds  define  the  outlines 
of  the  body. 

How  does  the  medullary  groove  develop  ? 

The  ridges  in  the  epiblast  on  either  side  continue  to  thicken,  and 
finally  coalesce  at  the  back,  leaving  a  lining  of  cells  within  a  tube. 
These  cells  develop  the  cerobro-spinal  axis  and  follow  the  curves 
of  the  blastoderm  longitudinally.  The  head  fold  gradually  becomes 
constricted,  and  becomes  the  neck.  Meanwhile  the  mesoblast  has 
developed  a  number  of  processes,  which  become  a  primitive  spinal 
column.  It  is  to  be  noticed  that  the  enclosure  of  the  spinal  canal 
in  this  way  is  by  a  folding  process,  and  all  through  the  process  of 
development  this  peculiarity  is  very  marked. 

What  is  the  mode  of  the  formation  of  the  pleuro-peritoneal  cavity  ? 
The  mesoblast  divides  near  the  median  line,  and  one  part  of  the 
split  mesoblast  adheres  to  the  epiblast,  while  the  remainder  joins 
the  hypoblast.  The  former  is  known  as  the  somatopleure,  and  the 
latter  as  the  splanchnopleure.  and  the  included  space  becomes  the 
pleuro-peritoneal  cavity,  which  subsequently  divides  to  form  pleura, 
pericardium,  and  peritoneum. 

What  structures  are  developed  from  the  epiblast? 

The  epidermis  and  appendages  of  the  skin,  the  great  nervous 
centres,  the  nerves,  and  the  principal  portions  of  organs  of  special 
sense — eye,  ear,  nose. 

What  does  the  hypoblast  develop? 

The  epithelial  elements,  including  the  glands  and  the  mucous 
membranes  lining  the  alimentary  and  pulmonary  tracts. 

What  does  the  mesoblast  develop? 

The  bones,  muscles,  fascije,  and  connective  tissues  of  the  body. 
It  also  develops  the  vascular  system.  It  must  be  remembered  that 
very  early  in  the  embryonal  life  this  tissue  divides  to  join  witli  the 
epiblast  and  hypoblast,  and  we  can  therefore  understand  how  it 
may  develop  the  muscular  structures  of  the  intestinal   canal. 

What  is  the  destiny  of  the  splanchnopleure  ? 

The  splanchnopleure  (5',  Fig.  oit)  folds  in  over  the  romainder  of 
the  ovum,  and  .so  walls  off,  so  to  speak,  a  portion  of  the  vitellus  which 
communicates  freely  with  the  rest  of  the  yelk-sac.    Later  on,  after 


188 


EMBEYOLOGY. 


the  formation  of  the  amnion,  the  yelk-sac  forms  a  blind  pouch  which 
is  lined  by  hypoblast  and  has  an  external  covering  of  mesoblast 
(Fig.  59),  as  is  shown  at  6  in  the  accom- 
FiG.  59.  panying  cut.     The  upper  6  is  in  the  primi- 

tive gut,  which  derives  its  epithelial  ele- 
ments from  the  hypoblast  and  its  muscular 
and  serous  coverings  from  the  mesoblast. 

What  is  the  yelk-sac  then  called? 

The  umbilical  vesicle. 

What  is  the  function  of  the  umbilical 
vesicle  ? 
From  it  the  embryo  derives  its  suste- 
nance in  the  earlier  stages.  Early  in  the 
development  blood-vessels  begin  to  form, 
and  they  ramify  over  the  surface  of  the 
umbilical  vesicle  and  help  to  absorb  its 
contents. 


Transverse  Sections  through 
the  Embryo  Chick,  before 
and  some  time  after  the 
closure  of  the  medullary 
canal,  to  show  the  upward 
and  downward  inflections 
of  the  blastoderm  (after  Ee- 
mak)  on  the  third  day  in 
the  lumbar  region:  1,  uoto- 
chord  in  its  sheath ;  2,  me- 
dullary canal,  now  closed 
in;  3,  section  of  the  medul- 
lary substance  of  the  spinal 
cord;  4,  corneous  layer;  5, 
somatopleure  of  the  meso- 
blast ;  5',  splauchnopleure 
(one  figure  is  placed  in  the 
pleuro-peritoneal  cavity) ;  6, 
layers  of  hypoblast  in  the 
intestines,  spreading  also 
over  the  yelk  ;  4X5,  part  of 
the  fold  of  the  amnion  form- 
ed by  epiblast  and  somato- 
pleure. 


What  is  the  amnion? 

While  the  one  portion  of  the  split  meso- 
blast (splauchnopleure)  unites  with  the 
hypoblast  to  form  the  splanchnoblast  and 
alimentary  organs,  the  outer  layer  (soma- 
topleure) and  epiblast  are  united  to  form 
the  skin  and  walls  of  the  body  as  the  soma- 
toblast.  The  somatoblast  now  folds  in 
about  the  embryo.  It  must  be  remem- 
bered, however,  that  the  entire  globe  of 
the  ovum  is  lined  with  these  cells,  and 
that  in  folding  in  this  way  the  cells  are  in 
a  measure  raised  away  from  the  wall  of  the  ovum.  The  layers  of 
the  somatoblast  fold  back  until  they  meet  and  unite  behind  the 
embryo,  and  in  this  way  form  a  layer  of  membrane  which  lines 
the  ovum  and  another  layer  which  encloses  the  embryo  (Fig.  60). 
This  latter  layer  forms  the  amnion.  (This  is  better  understood 
by  reference  to  the  cuts.) 


What  is  the  use  of  the  amnion  ? 

It  covers  the  embryo  in  the  early  stages  very  closely,  but  soon 
becomes  distended  with  a  pale  watery  fluid,  and  serves  to  float 


DEVELOPMENT. 


189 


the  foetus  and  give  it  equal  mechanical  support  on  all  sides.  The 
outer  layer  of  the  amnion  becomes  very  thin  and  adheres  to  the 
chorion. 

Fig.  60.  Fig.  61. 


Fig.  go. — Diagram  of  the  Fecundated  Egg,  farther  advanced  :  a,  umbilical  vesicle ;  h,  am- 
niotic cavity  ;  c,  allantoi.s. 

Fig.  61.— Diagram  of  the  Fecundated  Egg,  with  allantois  nearly  complete:  a,  inner  lam- 
ina of  amniotic  fold;  b,  outer  lamina  of  amniotic  fold;  c,  point  where  the  amniotic 
folds  come  in  contact.  The  allantois  is  seen  penetrating  between  the  inner  and  outer 
lamina;  of  the  amniotic  tolds. 


Fio.  62. 


What  is  the  composition  of  the  amniotic  fluid  ? 

It  is  water  containing  small  quantities  of  albumin  and  urea. 

What  is  the  allantois? 

During  the  development  of  the  amnion  from  the  somatoblast 
a  change  has  occurred  in  the  splanchno- 
blast.  From  the  inferior  extremity  of 
the  included  portion  of  the  yelk-sac, 
which  is  to  become  intestine,  there  has 
budded  a  small  mass  which  develops 
rapidly,  following  the  outline  of  the 
amnion  (see  Figs.  GO,  Gl,  G2),  and  grows 
fast  to  its  chorion  layer.  This  structure, 
the  allantois,  soon  becomes  very  vascular 
and  carries  its  blood-vessels  to  the  chorion. 


What  is  the  function  of  the  allantois  ? 

It  nourishes  the  growing  embryo.  The 
chorion  has  already  become  tufted  with 
capillary  loops,  and  has  establi.shed  a 
connection  with  the  decidua  of  maternal 
growth.     As  the  vessels  of  the  allantois 


Diagram  of  the  Fecundated  Egg, 
with  the  allantois  fully  form- 
ed :  fl,  umbilical  vesicle ;  b,  am- 
nion ;  c,  allantois. 


communicate  more  and 


more  with  the  chorion,  the  embryo  derives  more  of  its  sustenance 


190  EMBRYOLOGY. 

from  the  motlier,  and  the  remains  of  the  yelk-sac  (umbilical  ves- 
icle) dwindle  as  the  need  is  less  and  the  substance  is  consumed. 
(See  Figs.  60,  61,  and  62.) 

What  structures  in  the  body  are  derived  from  the  beginning 
of  the  allantois  ? 
The  urinary  bladder  and  the  urachus,  an  impervious  cord  extend- 
ing from  the  bladder  to  the  umbilicus. 

How  is  the  chorion  made  up  ? 

It  consists  of  several  layers  which  fuse  into  one  vascular  mem- 
brane. The  allantois,  the  outer  layer  of  the  amnion,  and  the  vitel- 
line membrane  are  united  in  the  chorion.  As  the  embryo  develops 
the  vessels  of  the  chorion  become  thinner  on  the  side  toward  the 
uterine  cavity,  and  more  distinct  on  the  opposite  side.  This  change 
continiies  as  the  embryo  increases,  until  the  placenta  is  formed  by 
the  branching  of  the  embryonic  vessels  and  the  increase  of  the 
decidua  at  the  corresponding  point. 

What  changes  occur  in  the  uterus  in  developing  the  placenta  ? 

In  the  deeper  part  of  the  mucous  membrane  of  the  uterus  at  the 
implantation  of  the  chorion  there  are  hollowed  out  spaces  or  si- 
nuses in  the  tissues  which  communicate  both  with  a  maternal  vein 
and  an  artery  ;  that  is,  special  arrangements  are  made  for  the  rapid 
circulation  of  a  large  amount  of  blood  in  the  uterine  mucous  mem- 
brane at  the  placental  site.  At  the  same  time,  the  glandular  struc- 
tures of  the  uterine  mucous  membrane  are  increased,  and  the  fol- 
licles run  deeply  into  the  thick  and  succulent  tissues. 

How  do  the  villi  of  the  chorion  become  implanted  in  the  uterine 
wall  ? 

The  villi  dip  down  and  develop  new  tufts  of  capillaries  in  the 
deepened  crypts  of  mucous  membrane,  so  that  the  tufts  of  capil- 
laries of  the  chorion  may  be  said  to  resemble  in  a  way  a  glove  filled 
with  fcetal  blood  dipping  into  a  vessel  filled  with  maternal  blood. 

Does  the  blood  of  mother  and  foetus  actually  come  in  contact  ? 

No.  There  are  four  layers  of  cells  between  the  maternal  and 
the  foetal  blood:  1,  wall  of  chorion  capillary;  2,  cells  of  chorion  ; 
3,  cells  of  uterine  follicle ;  and  4,  wall  of  the  uterine  sinus. 

Do  the  tissues  of  the  placenta  maintain  an  exchange  of  mate- 
rial? 
Yes.     The  mother's  blood  furnishes  to  the  foetal  blood  food  and 


DEVELOPMENT. 


191 


oxygen,  and  in  turn  removes  tlie  earltonie  acid  and  oxcromentitious 
material  wliieh  the  fetus  must  lose  ;  that  is,  the  placental  circula- 
tion supplies  the  place  taken  in  after-life  by  the  alimentary  and  the 
respiratory  tracts. 

Does  the  entire  placenta  leave  the  uterus  immediately  after  the 
birth  of  the  chdld  ? 

No.  The  foetal  part  is  almost  all,  excepting  some  of  the  capil- 
lary tufts  which  are  torn  off,  discharged  in  the  after-birth  ;  but  the 
decidua  is  not  entirely  disposed  of  in  this  way,  the  portions  remain- 
ing being  in  part  absorbed  and  in  j)art  found  in  the  lochia  which 
occur  i'or  a  few  days  after  the  birth. 

What  is  the  appearance  of  the  placenta  ? 

It  appears  as  a  thick,  cake-like  disk  of  vascular  tissue.  Its  ma- 
ternal and  foetal  portions  arc  so  intermingled  that  they  cannot  be 
separated.     In  size  it  covers  about  one-third  of  the  uterine  wall. 

At  what  period  of  gestation  is  the  placenta  formed  ? 

At  about  the  third  month  of  pregnancy.  Before  that  time  tlio 
chorion  is  covered  by  the  decidua  reflexa  and  nourishes  the  embryo, 
but  as  the  placenta  becomes  more  developed  other  parts  of  the 
chorion  atrophy. 

From  what  tissues  is  the  umbilical  cord  formed  ? 

From  the  vascular  allantois,  which 
carries  the  arteries  and  vein.    It  has,  Fig.  63. 

however,  an  external  coating  of  the 
amnion  and  the  shrivelled  umbilical 
vesicle  and  its  duct  (Fig.  63).  How 
this  occurs  will  readily  be  seen  by 
reference  to  the  accompanying  cut. 

Why  do  the  maternal  vessels  not 
bleed  excessively  after  the  pla- 
centa is  torn  from  its  implan- 
tation ? 

There  is,  of  course,  a  loss  of  the 
blood  contained  in  the  uterine  sin- 
uses, but  the  general  balance  of  the 
circulation  is  not  disturbed  at  child- 
birth.    The  reason  for  this  is  the  oblique  entrance  of  the  placental 


Human  Embryo  anrt  its  Envelopes  at 
tlie  I'-nd  of  the  Tliinl  Month,  show- 
ing the  en  hi  rgeim-ut  of  the  amnion. 


192  EMBRYOLOGY. 

vessels.  They  enter  the  sinuses  at  an  angle,  and  are  therefore 
compressed  by  the  muscular  tissue  of  the  uterus  in  its  contracted 
state. 

How  is  the  vertebral  column  developed? 

Early  in  the  development  of  an  embryo  there  is  formed  beneath 
the  medullary  groove  in  the  mesoblast  a  thin  thread  of  soft  carti- 
lage known  as  the  chorda  dorsalis,  or  notochord.  This  soon  be- 
comes included  in  a  sort  of  fibrous  sheath,  and  is  the  primary  axis 
from  which  the  bodies  of  the  vertebrae  are  developed.  On  either 
side  of  the  notochord  are  developed  small  centres  which  subse- 
quently split.  These  are  the  protovertebrse.  From  these  are  de- 
veloped the  vertebrae  and  the  heads  of  the  ribs  by  the  inner  lat/er, 
and  by  the  outer  (or  posterior)  lai/er  the  muscles  and  skin  of  the 
back,  the  epidermis  being  derived  from  the  epiblast. 

How  do  the  protovertebrse  form  the  vertebrae? 

It  is  not  by  direct  ossification  of  the  protovertebra3.  but  they 
separate  in  such  a  way  that  adjacent  protovertebrae  each  contribute 
half  to  the  vertebra  formed.  That  is,  two  protovertebrae  form  parts 
of  two  vertebrae,  one  above  and  the  other  below,  and  also  form  a 
whole  vertebra  by  their  adjacent  portions. 

How  is  the  cranium  developed? 

By  the  prolongation  of  the  epiblast  over  the  protovertebrae  to  the 
cephalic  end  of  the  embyro.  Here  it  develops  three  segments,  cor- 
responding to  the  three  primary  vesicles  which  are  the  forerunners 
of  the  brain.  These  centres  of  ossification  are  at  the  base  of  the 
skull,  the  bones  of  the  vertex  being  developed  from  membranes. 

How  is  the  face  formed  in  the  embryo? 

At  the  head  fold  of  the  embryo  the  mesoblast  does  not  split  into 
two  parts,  as  below,  but  folds  in  from  the  side,  covered  without  and 
within  by  the  epiblast  and  hypoblast.  These  folds  develop  certain 
clefts  from  which  the  face  is  derived,  the  mesoblast  furnishing  the 
bone  and  muscle  structures,  and  the  epiblast  the  epidermis,  while 
the  hypoblast  gives  the  mucous  membrane  which  lines  its  cavities. 

Describe  the  cleft  which  develops  the  face. 

Immediately  below  the  anterior  cranial  vesicle  there  occurs  on 
either  side  a  cleft  in  the  lateral  fold  of  the  embryo  extending  to 
the  vesicle  for  the  eye.     In  the  space  of  this  cleft  there  is  devel- 


DEVEI.OP^rENT. 


193 


Fi(i.  <;4. 


Developmeut  during  First  Month. 


Oped  a  sort  of  secondary  cleavage  of  the  parts,  which  by  the  rapid 
growtli  of  the  parts  included  between 
the  clefts  resembles  a  budding  (Fig. 
64).  It  is  by  the  growth  of  these 
buds  or  processes  that  the  outline  of 
the  face  is  formed.  From  each  side 
sprouts  the  superior  maxillary  pro- 
cess, and  the  processes  unite  in  the  me- 
dian line,  meeting  the  nasal  or  inter- 
maxillary process  from  the  upper  bor- 
der of  the  cleft.  The  portion  below  is 
cut  off  by  a  branchial  cleft,  which,  be- 
coming the  mandibular  process,  forms 
the  lower  jaw. 

What  defects  in  the  face  are  due  to  faulty  development  of  these 
processes  ? 

When  the  processes  do  not  unite  as  they  should,  various  defects 
occur ;  most  common  are  those  about  the  mouth,  cleft  palate  and 
hare-lip,  by  failure  of  the  superior  maxillary  processes  to  unite  or 
by  failure  of  the  intermaxillary  process  to  unite  with  the  max- 
illary. 

Do  the  other  branchial  clefts  persist  in  later  life  ? 

No.  They  become  closed  as  they  accomplish  their  use  in  devel- 
oping certain  organs  :  as  pathological  factors,  however,  we  are  often 
convinced  of  their  non-union  or  of  flaws  in  their  development,  cysts 
and  tumors  of  various  kinds  and  certain  fistula)  being  attributable 
to  this  cause. 

How  are  the  extremities  developed? 

They  develop  as  buds  from  the  somatoblast  early  in  foetal  life, 
and  the  formation  of  the  joints  and  lesser  details  of  structure  are 
gradually  worked  out.  At  about  the  third  month  the  separation 
of  the  fingers  and  division  of  the  extremity  into  joints  is  about 
completed.  The  arm  develops  somewhat  in  advance  of  the  leg,  and 
grows  rather  more  rapidly  in  the  earlier  period  of  intra-uterine  life. 

What  two  forms  of  circulation  are  found  in  the  embryo  ? 

The  earliest  is  the  vitelline  circulation,  in  which  vessels  from  the 
foetus  pass  over  the  yelk-sac  and  carry  nutrition  to  the  growing- 
organism.     There  is  formed  a  placental  circulation,  in  which  the 
maternal  blood  furnishes  the  elements  of  food. 
13— Phy. 


194  EMBRYOLOGY. 

What  is  the  vascular  area  (area  vasculosa)  of  the  foetus  1 

Among  the  earliest  changes  in  the  blastoderm,  occurring  in  the 
second  week  of  impregnation,  is  the  formation  of  blood-vessels 
and  blood-corpuscles.  This  occurs  by  the  proliferation  of  certain 
branched  cells  of  the  mesoblast,  and  these  cells  form  a  closed  sys- 
tem of  branching  capillaries,  their  nuclei  acquiring  a  red  color 
and  becoming  the  blood-corpuscles.  This  area  is  external  to  but 
connected  with  the  embryo. 

How  is  the  heart  formed  ? 

At  about  this  time  certain  cells  of  the  visceral  layer  of  the  meso- 
blast (splanchnopleure)  develop  a  tube  upon  each  side  of  the  body, 
and  these  two  tubes  soon  coalesce  to  form  a  single  tube  (Fig.  65), 
which  receives  two  veins  at  its  lower  end  and  gives  off  two  arteries 
at  its  upper.    This  is  the  primitive  heart,  and  pulsations  begin  in  it 

very  feebly  almost  as  soon  as  there  is 
Fig.  65.  Fig.  66.  a  trace  of  the  originating  cells.      This 

2  ..2  structure  soon  develops  a  muscular  tis- 

I  I  -i  -^^  X  ^  ^^^'  ^^'^  ^  circulating  fluid  which  short- 

ly presents  the  character  of  blood. 


What  is  the  next  important  change 
in  the  form  of  the  heart  ? 

'1^  I '  '    \>^_^  It  bends  itself  so  as  to  assume  a  U- 

FiG.  65.— Earliest  Form  of  the  Foe-     shape,  which  shortly  is  twisted  in  such 
tai  Heart:  1  venous  extremity;     manner  that  the  arterial  end  of  the 

2,  arterial  extremity.  •       r.  r>      i 

Fig.  66.— Foetal  Heart  bent  upon     heart  crosses  in  front  of   the  venous 
Siki'4x?remity.'"'""^*''  ''     (Fig-  66),  and  the  loop  suggests  the 

outline  of  the  ventricles.  The  vitel- 
line circulation  in  the  human  ovum  is  not  very  long-lived,  for  the 
chorion  is  early  formed  and  the  stock  of  nutrient  protoplasm  in  the 
yelk-sac  is  very  small. 

What  further  modifications  does  the  heart  undergo  ? 

The  septum  between  the  ventricles  grows,  and  separates  the 
heart  into  two  divisions  ;  and  at  about  the  same  time  the  auricles 
are  developed  and  the  valves  become  well  marked.  These  changes 
occur  in  the  fourth  to  the  eighth  week  of  embryonic  life. 

Describe  the  vitelline  circulation. 

The  area  vasculosa  extends  all  about  the  blastoderm  upon  the 


DEVELOPMENT. 


195 


Fi<;.  G7 


surface  of  the  vitcUus.  and  as  the  folds  of  the  embryo  occur  the 

vessels   are   brought  to   enter  the   body 

throuirh   the    space    at  which   the   vitel- 

lus  is  shut  in  to  form  the  primitive  gut. 

There  are  then  two  arteries  and  two  veins, 

which  are  known  as  the  omphalo-mesen- 

teric  vessels.  This  form  of  circulation  soon 

gives  way  to  the  jilacental,  and  the  vessels 

passing  to  the   umbilical  vesicle   waste, 

those   belonging   to   that  portion  of  the 

original  vitelline  cavity  which  forms  the 

intestine,  becoming  the  mesenteric  vessels. 

What  are  the  prominent  features  of  the 
placental  circulation? 

(1)  In  the  arterial  circulation  some 
conditions  of  the  heart  and  great  ves- 
sels are  necessary  to  modify  the  pulmo- 
nary circulation  before  the  air  enters  the 
lungs  at  birth.  (2)  In  the  circulation  of 
the  liver  the  veins  present  modifications  to  allow  for  the  return 
placental  circulation. 

Where  do  the  arteries  to  the  placenta  arise? 

They  follow  the  allantois  in  its  growth.  Springing  from  the 
internal  iliac  artery  of  each  side,  two  arteries  pass  up  the  umbilical 
cord  and  break  into  the  branches  in  the  placenta  which  terminate 
in  capillar}-  tufts. 

How  does  the  blood  return  to  the  body  from  the  placenta? 

By  the  umbilical  vein  it  is  taken  to  the  liver,  where  part  of  it  cir- 
culates through  the  liver-capillaries  in  the  same  manner  as  the  blood 
from   the  portal  vein,  the  remainder  passing  through  the   ductus 


Diagram  of  the  F,ml)ryo  and  its 
Vessels,  showing  the  circula- 
tion of  the  uniliilical  vesicle, 
and  also  that  of  the  allantois, 
beginning  to  be  formed. 


What  is  the  ductus  venosus? 

It  is  a  large  vein  which  appears  at  the  under  surface  of  the 
liver,  and  returns  a  large  part  of  the  blood  from  the  umbilical 
vein  directly  to  the  inferior  vena  cava,  without  circulation  in  the 
capillaries  of  the  organ. 
How  does  the  ductus  venosus  appear  in  adult  life? 

Soon  after  birth  the  umbilical  vein  and  ductus  venosus  become 
an  impervious  cord  extending  from  the  navel  to  the  liver :   the 


1 96  EMBRYOLOGY. 

former  becomes  the  round  ligament  of  the  liver,  while  the  ductus 
venosus  remains  as  a  small  fibrous  cord. 

What  is  the  course  of  the  foetal  blood  through  the  heart  ? 

It  enters  the  right  auricle,  and  is  thence  sent  in  part  to  the 

right  ventricle,  and  in  part  to  the  left  auricle, 

Fig.  68,  through  the  foramen  ovale,  an  opening  left 

in  the  development  of  the  auricular  septum. 

The  blood  which   enters   the   left  ventricle 

from  the  left  auricle  is  forced  out  through 

the   aorta   (Fig.    68).      The  right  ventricle, 

however,  sends  but  a  small  part  of  its  blood 

to  the   lungs,  but   delivers   it   through   the 

ductus  arteriosus  to  the  aorta.     The  blood  is 

in  this  way  sent  into  the  systemic  circulation, 

Foetal  Heart  still  farther     a  part  going  to  the  placenta  through  the  inter- 

pui.nonary  arteTy fs,  l\     "^^  ^^1^^,  hypogastric,  and  umbilical  arteries. 

pulmonary  branches ;  4,      ttn.    ^     re     j.  i         1.1       ■nj.-i.'  1 

ductus  arteriosus.  What  effect  has  the  Eustachian  valve  upon 

the  blood-stream  in  the  foetal  heart  ? 

It  throws  the  blood  from  the  inferior  vena  cava  through  the 
foramen  ovale  into  the  left  auricle.  In  this  way  the  stream  of 
blood  coming  from  the  superior  vena  cava  crosses  that  from  the 
inferior  cava  on  entering  the  heart,  inasmuch  as  the  blood  from 
the  superior  vena  cava  enters  the  right  ventricle. 

What  effect  does  this  division  of  the  blood-stream  have  upon  the 
distribution  of  the  blood  in  the  foetus  ? 
The  circulation  of  the  blood  is  made  more  perfect,  for  the 
branches  of  the  aorta  given  off  to  the  head  and  upper  extremities 
distribute  blood  from  the  inferior  vena  cava ;  while  the  ductus 
arteriosus,  carrying  the  blood  from  the  superior  cava  and  right 
ventricle,  enters  the  aorta  in  such  a  way  that  most  of  its  blood  is 
sent  to  the  lower  extremities  and  abdominal  organs  and  umbilical 
arteries.  In  this  way  the  deoxidized  blood  is  sent  back  to  the 
placenta  for  the  renewal  of  its  oxygen. 

How  does  this  result  in  the  development  of  the  lower  extrem- 
ities ? 
They  develop  less  rapidly  than  the  upper.  There  are  probably 
two  reasons  for  this:  1,  the  blood  is  less  well  aerated  and  less 
nutritious ;  2,  the  internal  iliac  arteries,  giving  off  the  umbilical 
arteries,  probably  divert  a  considerable  portion  of  the  blood-supply 
of  the  external  iliacs  which  go  to  the  lower  extremities. 


DEVELOPMENT.  197 

What  changes  occur  in  the  circulation  after  the  birth  of  the 
foetus  ? 

The  respiratory  centre  in  the  medulhi,  whicli  has  been  quiescent 
because  it  lias  been  sufficiently  well  supplied  with  oxygen,  is 
awakened  as  soon  as  the  connection  with  the  uterine  sinuses  is 
interrupted.  As  soon  as  the  supply  of  oxygen  sinks  to  a  certain 
point,  an  impulse  of"  inspiration  is  generated,  and  the  infant  breathes 
and  the  lungs  assume  a  condition  of  partial  expansion.  With  the 
diminished  resistance  in  the  expanded  lungs  the  amount  of  blood 
in  the  pulmonary  circulation  increases,  and  the  amount  passing 
through  the  ductus  arteriosus  diminishes,  and  this  is  soon  obliterated. 
At  the  same  time,  the  blood  returning  to  the  left  auricle  increases 
in  quantity,  and  the  intra-auricular  pressure  is  greater ;  then,  too, 
the  inferior  vena  cava  sends  less  blood,  for  the  ductus  venosus  no 
longer  carries  the  blood  from  the  placental  circulation,  and  there- 
fore the  foramen  ovale  is  not  used,  and  is  soon  closed  by  the 
adhesion  of  its  valve-like  curtain.  Thus  we  have  the  adult  circu- 
lation established  in  the  place  of  the  foetal  in  consequence  of  the 
respiratory  movements. 

How  is  the  spinal  cord  formed? 

It  will  be  remembered  that  the  medullary  canal  encloses  in  its 
cavity  cells  from  the  epiblast  which  line  it.  These  cells  by  pro- 
liferation and  differentiation  develop  nerve-cells  and  nerve-fibres, 
the  latter  at  first  not  medullated.  The  cells  also  gradually  close  in 
upon  the  medullary  canal,  and  form  a  central  canal  lined  with 
epithelium,  a  layer  of  nerve-cells  (gray  matter),  and  a  layer  of 
nerve-fibres  (white  matter). 

How  do  we  account  for  the  obliquity  of  the  spinal  nerves  and  for 
the  Cauda  equina? 
When  the  spinal  cord  first  appears  it  fills  the  entire  spinal  canal, 
but  at  the  time  of  birth  the  cord  has  apparently  not  grown  so 
rapidly  as  the  vertebral  column,  for  it  then  ends  at  the  third 
lumbar  vertebra,  and  in  the  adult  it  ends  at  the  first.  Thus  we 
are  able  to  explain  the  apparent  origin  of  the  spinal  nerves  above 
their  point  of  exit  from  the  canal,  and  the  increasing  obliquity  of 
the  nerves  from  above  down,  until  finally,  in  the  tuft  of  vertical 
nerves  below  the  extremity  of  the  cord,  we  see  the  extreme  degree 
of  this  peculiarity. 

How  do  the  spinal  nerves  develop? 

They  are  formed  from  cells  arising  from  the  epiblast  lining  the 


198 


EMBRYOLOGY. 


medullary  groove.  Before  the  closure  of  this  groove  to  form  the 
medullary  canal  an  offshoot  from  the  epiblast  may  be  observed, 
which  is  the  source  of  the  posterior  nerve-roots ;  and  they  become 
attached  to  the  cord  as  it  develops.  The  anterior  roots  spring  from 
the  cord  after  it  has  developed  fibres.  The  two  roots  then  join  and 
the  nerve  grows  out  into  the  mesoblast. 

Are  the  cranial  nerves  similarly  derived  ? 

In  much  the  same  way  the  cranial  nerves  arise  primarily,  except 
the  nerves  of  special  sense.  In  function  the  motor  nerves  seem  to 
form  a  sort  of  anterior  root  for  the  sensory,  so  that  they  may  be 
arranged  in  pairs  corresponding  to  the  anterior  and  posterior  roots 
of  the  spinal  nerves  ;  and  it  does  not  seem  entirely  fanciful  to  re- 
gard their  development  as  somewhat  similar,  thus  : 

Third,  fourth,  sixth,  and  seventh  motor,  fifth  sensory.  Twelfth 
motor,  ninth  sensory.     Eleventh  motor,  tenth  sensory. 

How  does  the  earliest  rudimentary  brain  appear? 

The  medullary  canal  is  widened  from  the  very  beginning  at  its 
anterior  end,  and  very  early  develops  three  ves- 
icles, which  are  shown  diagrammatically  in  Fig. 
69.  These  vesicles,  with  their  lining  of  epiblast, 
are  the  primitive  brain. 

How  does  the  anterior  cerebral  vesicle  become 
changed  ? 

This  vesicle  is  destined  to  become  the  third  ven- 
tricle of  the  brain,  and  from  its  anterior  surface 
are  developed  two  protrusions  which  expand  to 
form  the  hemispheres  of  the  brain  ;  thus,  this  ves- 
icle is  early  divided  into  two  parts,  the  fore-brain 
or  prosencephalon,  and  the  inter-brain  or  thalam- 
%  encephalon. 

I  What  is  the  middle  primary  vesicle  called  ? 

I  The    mesencephalon.       It    corresponds    to    the 

'  aqueduct  of  Sylvius. 

How  is  the  posterior  vesicle  altered  ? 

This  is  destined  to  become  the  fourth  ventricle, 
and  by  a  similar  protrusion  it  develops  a  second 


Fig.  69. 


Formation  of  the  Ce- 
rebro-spiual  Axis: 
1,  vesicle  of  the 
hemisphere ;  2,  ves- 
icle of  the  tubercu 


la  quadrigeinina ;  3,  portion,  which   becomes    the   cerebellum.     These 
duiia  oblongata,      divisions   of   the    posterior   cerebral   vesicle    are 


DEVELOPMENT. 


199 


I.  Anterior 
primary 
vesicle. 

II.  Middle 
primary 
vesicle. 

III.  Posterior 
primary 
vesicle. 


known   as  the  epencephalon,  and  the  after-brain,  or  metenceph- 
alon. 

"What  parts  of  the  brain  do  these  five  vesicles  respectively  orig- 
inate? 

(  Cerebral  hemispheres,  cor- 
pora striata,  corpus  callo- 
sum,  fornix,  lateral  ven- 
tricles, olfactory  bulb. 

f  Thalami  optici,  third  ven- 

I     tricle,  optic  nerve. 

"  Corpora  quadrigemina, 
crura  cerebri,  aqueduct 
of  Sylvius. 
Cerebellum,  pons  Varolii, 
anterior  part  of  fourth 
ventricle. 
Medulla  oblongata,  fourth 
ventricle,  auditory  nerve. 


1.  Prosencephalon. 

j  2.  Thalamencephalou. 
[  3.  Mesencephalon. 

4.  Epencephalon. 

5.  Metencephalon. 


What  is  the  primary  optic  vesicle  ? 

About  as  soon  as  the  cerebral  vesicles  are  distinctly  formed  a 
budding  of  two  projections — one  from  either  side  of  the  anterior 
vesicle — occurs.  These  are  the  primary  optic  vesicles.  They  are 
formed  before  the  vesicles  which  make  the  hemisphei'es  (prosen- 
cephalon). The  projections  approach  the  external  epiblast,  and  at 
that  period  consist  of  a  finger-like  process  having  a  globular  dilata- 
tion at  the  end.  This  subsequently  forms  the  optic  nerve  and  the 
retina. 

How  is  the  crystalline  lens  formed? 

Opposite  the  optic  vesicle  the  superficial  epiblast  is  depressed 
and  forms  a  sort  of  pit.  forcing  the  optic  vesicle  to  fold  in  upon 
itself.  The  follicle  of  epiblast  is  shut  off  at  the  surface,  and  a  ball 
of  its  substance  left  in  the  cup  of  the  infolded  optic  vesicle.  This 
ball  forms  the  rudimentary  lens,  and  the  anterior  layer  of  the  ves- 
icle is  the  retina. 

How  are  the  other  tissues  of  the  eye  evolved  ? 

The  muscular  and  vascular  structures,  as  well  as  the  connective 
tissue  and  humors,  are  derived  from  the  mesoblast.  which  in  part 
enfolds  the  ocular  vesicle  and  in  part  enters  it  between  the  lens 


200i  EMBRYOLOGY. 

and  the  edge  of  the  cup-like  depression.     The  cornea  is  of  later 
formation,  and  is  derived  from  the  epiblast  of  the  skin. 

How  is  the  auditory  apparatus  developed  ? 

Very  early  in  the  life  of  an  embryo  there  is  a  depression  on 
either  side  of  the  head  which  passes  through  the  same  process  as 
that  mentioned  for  the  crystalline  lens  and  for  the  germinal  epi- 
thelium in  the  formation  of  ova.  The  mass  of  epiblast  thus  sepa- 
rated forms  the  epithelium  of  the  labyrinth  and  vestibule,  the 
surrounding  mesoblast  furnishing  the  bony  and  muscular  structures. 
The  auditory  nerve  is  developed  with  other  cranial  nerves,  and 
grows  in  to  its  end-organs  from  its  central  origin. 

How  is  the  olfactory  apparatus  derived? 

In  a  similar  way  to  the  internal  ear  and  the  lens.  The  nasal  fossa 
is  primarily  a  depression  in  the  superficial  epiblast,  which  widens 
and  deepens  and  receives  the  nerve-filaments  from  the  olfactory 
lobe.  This  lobe  is  originally  a  bud  from  the  prosencephalon.  The 
primary  olfactory  depression  continues  to  widen  until  it  opens  into 
the  mouth,  and  is  again  shut  off  by  the  growth  of  the  branchial 
arch,  which  forms  the  superior  maxilla.  The  nose  is  similarly 
derived  from  the  mesial  and  lateral  nasal  processes. 

Describe  the  method  of  the  development  of  the  alimentary  canal. 

As  has  already  been  explained,  the  primitive  alimentary  canal  is 
formed  from  the  involution  of  the  splanchnopleure,  and  is  really  a 
portion  of  the  yelk-sac  partially  shut  off  from  the  rest.  It  is  at 
each  end  a  blind  pouch  which  follows  the  head  and  tail  folds. 
The  portions  have  received  the  names  fore-gut  and  hind-gut  as  they 
occupy  one  or  other  of  these  folds. 

How  does  the  fore-gut  become  changed? 

It  joins  with  the  mouth-cavity  by  the  folding  back  of  the  epi- 
blast in  the  formation  of  the  branchial  arches,  and  from  it  are 
formed  the  pharynx,  oesophagus,  and  stomach. 

How  does  the  hind-gut  approach  the  surface  ? 

By  a  similar  involution  of  the  epiblast  the  anus  and  about  half 
of  the  rectum  are  formed,  into  which  the  hind-gut  opens  to 
complete  the  alimentary  tract. 

What  deformities  in  the  new-born  depend  upon  the  defective 
accomplishment  of  these  changes  ? 
The  oesophagus  is  sometimes  impervious  at  birth,  and  the  rectum 


DEVELOPMENT.  201 

or  anus  may  also  be  imperforate.  This  is  caused  by  the  non-union 
of  the  segments  developed  from  the  epiblast  with  those  developed 
from  the  hypoblast. 

How  are  the  glands  of  the  alimentary  tract  developed  ? 

(1)  The  Hulivdry  glaiuh  are  developed  from  the  epiblast  lining  the 
oral  cavity.  They  appear  primarily  as  a  simple  tube  which  devel- 
ops branches,  about  which  the  alveoli  are  formed. 

(2)  The  pancreas  is  similarly  developed  from  the  hypoblast  of 
the  fore-gut. 

(3)  The  liver  is  primarily  a  protrusion  of  the  hypoblast  of  the 
fore-gut,  which  appears  as  soon  as  the  blood-vessels  begin  to  show 
themselves.  The  omphalo-mesenterie  vein,  from  the  umbilical 
vesicle,  breaks  up  into  a  capillary  plexus,  and  the  hepatic  cells 
develop  about  it. 

How  are  the  lungs  derived? 

They  first  appear  as  a  bud  at  the  junction  of  pharynx  and 
oesophagus  which  soon  forms  a  separate  tube  (the  trachea).  The 
cells  from  the  hypoblast  extend  into  the  surrounding  mesoblast, 
and  it  is  from  this  structure  that  all  of  the  tissue  of  the  lungs, 
except  its  mucous  membrane,  are  formed. 

What  is  the  Wolffian  body? 

It  is  a  rounded  body  which  is  first  seen  as  early  as  the  third 
week  as  an  increase  of  the  cells  of  the  mesoblast,  just  inside  of 
its  division  into  parietal  and  visceral  layers,  on  each  side  of  the 
vertebral  column.  It  is  soon  seen  to  consist  of  three  parts,  from 
which  are  derived  the  genito-urinary  organs.  The  largest  of  these 
in  early  embryonic  life  retains  the  name  Wolffian  hodij,  and  is  not 
a  permanent  organ  ;  a  second,  lying  just  above,  develops  the  internal 
organs  of  generation  ;  while  the  third,  lying  behind  the  Wolfl&an 
body,  is  the  rudimentary  kidney. 

What  is  the  function  of  the  Wolffian  body  ? 

The  Wolffian  body  proper — that  is,  after  its  division  into  three 
sections — is  a  temporary  kidney.  At  first  this  is  a  large  glandular 
body,  resembling  the  kidney  in  structure,  which  possesses  a  duct 
leading  to  and  opening  into  the  hind-gut.  At  about  the  sixth 
week  of  foetal  life  the  kidney  begins  to  grow  and  the  temporary 
organ  to  atrophy.  As  this  occurs  a  duct  for  the  kidney  (the 
ureter)  is  developed   from    the   "Wolfliian  duct.     The   use  of  the 


202  EMBRYOLOGY. 

organs  seems  to  be  that  of  temporary  kidneys,  but  by  the  end  of 
the  third  month  they  have  been  replaced  by  the  permanent  organs, 
and  have  almost  entirely  disappeared. 

How  do  the  testicle  and  ovary  originate  ? 

The  body  (germinal  epithelium)  which  appears  on  the  inner  side 
of  the  Wolffian  body  is  the  nucleus  of  the  future  testicle  or  ovary, 
while  from  the  outer  side  there  springs  a  duet  (Mtiller's)  which 
passes  down  to  the  cloaca  or  lower  end  of  the  hind-gut.  At  first  it 
is  impossible  to  determine  the  sex  of  the  foetus. 

How  do  the  remaining  genital  organs  of  the  female  develop  ? 

The  ducts  of  Mtiller  join  to  form  the  uterus  and  vagina,  while 
the  ununited  portions  remain  as  the  Fallopian  tubes.  The  AVolffian 
ducts,  which  also  spring  from  the  Wolffian  bodies,  are  rudimentary 
in  the  female  and  appear  as  a  part  of  the  parovarium. 

How  do  the  remaining  male  organs  of  generation  develop  ? 

The  Wolffian  ducts  become  convoluted  tubules,  and  each  is  at- 
tached to  the  testis  as  the  epididymis.  Mtiller's  duct  is  rudimentary 
in  the  male,  and  is  only  found  as  the  sinus  pocularis  and  the  hy- 
datids of  Morgagni. 

How  are  the  external  genitals  formed  ? 

In  both  sexes  in  early  foetal  life  the  external  genitals  are  alike, 
consisting  of  a  body  resembling  a  penis  with  a  fold  of  skin  at 
either  side.  In  the  female  this  body  becomes  proportionately 
smaller,  and  appears  as  the  clitoris,  the  two  lateral  masses  becom- 
ing the  labia  majora.  In  the  male  a  groove  on  the  under  surface 
unites  at  its  borders  to  form  the  urethra,  while  the  scrotum  is  formed 
from  the  folds  of  skin  at  the  side.  This  differentiated  condition  may 
persist  in  adult  life,  and  has  been  mistaken  for  hermaphroditism. 

PARTURITION. 

How  is  the  foetus  extruded  from  the  uterus? 

In  part  by  the  contraction  of  the  uterine  muscles,  and  in  part  by 
the  pressure  exerted  by  the  abdominal  walls.  The  uterine  contrac- 
tions are  the  first  to  appear,  and  it  is  not  until  the  foetus  enters  the 
vagina  that  the  abdominal  muscles  are  brought  into  play. 

What  causes  excite  the  uterine  contractions? 

As  to  this  no  satisfactory  answer  has  been  given.     Why  the 


PARTURITION.  203 

uterus  should  contain  the  o-rowing  embryo  for  months,  and  then 
be  suddenly  tlirown  into  action  to  expel  it,  cannot  be  explained. 

What  is  the  nature  of  the  act  of  parturition  ? 

It  is  a  reflex  action  (lepeiidiiii;-  u])on  a  centre  in  the  lumbar  spi- 
nal cord.  Whence  the  stimuli  are  derived  which  excite  the  reflex 
is  unknown,  but  probably  from  the  organ  itself". 

What  is  the  character  of  the  uterine  contractions  ? 

They  are  rhythmical  in  character,  and  may  be  compared  to  the 
contractions  of  the  heart-muscle.  P]acli  "  pain  "'  begins  feebly,  grad- 
ually intensifies  until  it  reaches  a  maximum,  and  then  gradually 
declines  until  it  entirely  dies  away,  to  be  succeded  by  another  simi- 
lar contraction  and  pause.  This  rhythmical  action  continues  until 
the  utei'inc  contents  are  expelled,  and  then  the  organ  enters  into  a 
condition  of  tonic  contraction. 


APPENDIX. 


TABLE   OF   THE   DEVELOPMENT  OF    AN  EMBRYO. 

(Modified  from  Gray's  Anatomy.) 

Isf  WecJc. — Ovum  in  Fallopian  tube.     Segmentation  of  vitellus. 

2d  Week. — Ovum  in  uterine  decidua.  Chorion.  Formation  of  blasto- 
derm and  division  of  mesoderm.  Heart  and  medullary  groove.  Amnion 
and  umbilical  vesicle  formed.     xVllantois. 

3d  Week. — Head  and  tail  flexures.  Closure  of  medullary  canal,  and 
formation  of  primary  cerebral  vesicles  and  ocular  and  auditory  vesicles. 
Branchial  ai'ches.     Wolffian  bodies.     Limbs. 

4th  Week. — Limbs  increased.  Anal  opening.  Interventricular  sep- 
tum begins.    Ant.  spinal  nerve-roots.    Olfiictory  fosste.    Lungs.    Plem-as. 

5th  Week. — Allantois  vascular.  Trace  of  feet  and  hands.  Miiller's 
duct  and  genital  gland. 

6th  Week. — Umbilical  vesicle  disused.  Branchial  clefts  close.  Post- 
spinal  nerve-roots.  Membranes  of  the  nervous  centres.  Bladder.  Kid- 
neys.    Tongue.     Larynx. 

7th  Week. — Muscles  perceptible.    Many  centres  of  ossification  appear. 

8th  Week. — Joints  appear  in  extremities;  fingers  and  toes  separate. 
Crystalline  lens.  Salivary  glands.  Spleen.  Interventricular  septum 
complete.     Sympathetic  nerves. 

9th  Week. — Distinction  between  ovary  and  testicle.  Genital  furrow. 
Pericardium. 

3d  Month. — Formation  of  placenta.  External  genitals  separate  from 
anus.     E.yelids,  hairs,  and  nails.     Duct  of  Wolffian  body  joins  testicle. 

Jfth  Month. — Middle-ear  bones.  Tympanum  and  labyrinth.  Scrotum 
and  prepuce. 

5th  Month. — Germs  of  teeth.  Hair-  and  sweat-glands.  Brunner's 
glands.     Uterus  and  vagina  distinctly  separate. 

6th  Month. — Papillfe  of  skin.  Sebaceous  glands.  Pej-er's  patches. 
Free  border  of  nails. 

7th  Month. — Cerebral  convolutions.     Pupillary  membrane  disappears. 

8th  Month. — Descent  of  testis. 

9th  Month. — Opening  of  eyelids.     Ossification  of  cochlea. 

CHEMICAL     TESTS     USED     COMMONLY    IN    PHYSIO- 
LOGICAL  ANALYSIS. 
For  Proteids  : 
Nitric  Acid  coagulates  all  except  peptones. 

P  206 


206  APPENDIX. 

Heat. — All  are  coagulated  by  boiling,  except  peptones. 

Xanthoproteic  Reaction. — A  solution  boiled  with  strong  nitric  acid 
becomes  yellow :  the  color  is  deepened  by  the  addition  of  ammonia. 

Biuret  Reaction. — With  a  trace  of  copper  sulphate  and  an  excess  of 
potassium  or  sodium  hydrate  they  give  a  purple  reaction. 

union  s  Reaction. — With  a  solution  of  metallic  mercury  in  strong 
nitric  acid  (Millon's  reagent)  they  give  a  white  or  pinkish  reaction,  and 
the  color  becomes  more  pink  on  boiling. 

For  Starch: 

_  Iodine  Reaction. — Add  to  a  solution  of  starch  a  small  quantity  of 
tincture  of  iodine,  and  a  blue  reaction  results.  The  color  disappears  on 
heating  and  returns  on  cooling. 

_  Glycogen. — Same  test  gives  reddish  reaction,  port-wine  color,  which 
disappears  on  heating  and  returns  on  cooling. 

For  Sugar  (Glucose)  : 

Moore's  Test. — Boil  solution  of  sugar  with  an  excess  of  potassium 
hydrate,  brown  color-reaction. 

Trommer''s  ^es^.— Add  to  solution  a  sufficient  amount  of  potassium 
hydrate  to  render  it  quite  strongly  alkaline.  Then  add  a  solution  of 
copper  sulphate,  drop  by  drop,  until  a  distinct  blue  tinge  is  visible. 
Heat,  and  the  presence  of  sugar  is  shown  by  appearance  of  red,  yellow, 
or  orange  color-reaction. 

Felilings  Test  Solution. — An  alkaline  copper  solution  by  which  a 
quantitative  test  may  be  made.  The  solution  is  somewhat  unstable,  and 
is  for  this  reason  to  be  tested  by  boiling  before  using.  The  strength  of 
the  solution  is  such  that  1  cubic  cm.  (15  minims)  will  be  exactly  decolor- 
ized by  2^0  of  a  gramme  (.075  grains)  of  glucose.  This  test  is  very 
delicate,  and  is  quite  commonly  used  for  urinary  examinations  to  detect 
glycosuria. 

The  Fermentation  Test. — If  a  small  quantity  of  yeast  be  added  to  a 
sugar  solution,  the  fungus  of  the  yeast  (saccharomyces)  will  cause  the 
sugar  to  be  decomposed  into  carbonic  acid  and  alcohol.  If  the  process 
be  continued  until  the  sugar  is  entirely  broken  up,  the  amount  of  car- 
bonic acid  evolved  indicates  the  proportion  of  sugar  present. 

For  Bile  Salts  : 

Pettenlwfer  s  Test.  — Upon  the  addition  of  sulphuric  acid  to  a  solution 
of  bile-salts  in  water  thei'e  is  a  precipitation  of  the  salts,  which  are 
redissolved  by  a  further  addition  of  the  acid.  If  a  drop  of  a  solution 
of  cane-sugar  be  added,  a  deep  cherry  color  is  developed. 

For  Bile  Pigments: 

Gmelins  Test. — Add  a  small  quantity  of  nitroso- nitric  acid  to  a  solu- 
tion of  the  bile-pigments,  and  a  play  of  colors  results,  beginning  with 
green  and  changing  to  blue,  violet,  red,  and  yellow.  This  is  seen  best 
on  a  white  background ;  therefore  a  plate  is  often  used  for  this  test. 


MIIIIU 

Millimetres. 


APPENDIX. 
METRIC   SYSTEM. 


I     I     I     I     I     I     I     '  1  Tncli 


(uiiUmc'lros. 


I  3 


207 


ID 


The  area  of  the  figure  within  the  heavy  lines  is 
that  of  a  square  decimetre.  A  cube  one  of  whose 
sides  is  this  area  is  a  cubic  decimetre  or  litre.  A 
litre  of  water  at  the  temperature  of  4°  C.  weighs  a 
kilogramme. 

A  litre  is  1.76  p?««;  a  pint  is  0.508  of  a  litre. 

The  smaller  figures  in  dotted  lines  represent  the 
areas  of  a  square  centimetre  and  of  a  squre  inch. 

A  cubic  centimetre  of  water  at  4°  C.  weighs  a 
gramme. 


Square 
Centi- 
metre. 


Metre  =  39f  inches. 
Centimetre  =  f  inch. 
Millimetre  =  ^V  inch. 
Micromillimetre  =  25000  inch. 

Gramme  =  15^  grains. 
Centigramme  =  -^^  grain. 
Milligramme  =  ^f^a  grain. 
Kilogramme  =  2.2  pounds. 


INDEX 


A. 

Absorption,  59-62 
Accommodation,  16fj,  166 
After-images,  172 
Air:  changes  in  the  lungs,  40 

composition,  39 

course  in  lungs,  37 

expired,  39 
water,  39 

introduction,  37 

nitrogen,  40 

reserve,  38 

temperature,  39 

tidal,  38 
Allantois,  189,  190 
Amnion,  1S3 
Amylopsin,  54 
Auinial  heat,  62,  63 
Appendix,  205 

chemical  tests  (table),  205,  206 

embryonal  development  (table),  205 

metric  system,  207 
Area  vasculosa,  194 
Areas,  motor,  128 

sensory,  128 
Arrest  of  action,  104 
Arterial  tension,  36      * 
Arteries,  30 
Astigmatism,  167 
Atmosphere,  composition,  39 
Automatic  action,  99,  113 

B. 

Bile,  flow,  55 

ingredients,  56 

quantity,  56 

uses,  58 
Blastoderm,  184 

changes.  185,  186 
Blind  spot,  167,  168 

14 


Blood,  22 

arterial,  26 

character,  22 

chemical  bases,  27 

circulation,  27 

clot,  22 

coagulation,  23,  24 

corpuscles,  24 

gases,  27 

lack  of  oxygen,  41 

menses,  26 

quantity,  22 

uses,  26 
Body  expenditure,  90,  91 

income,  90,  91 
Branchial  clefts,  193 

c. 

Capillaries,  30 
Capillary  force,  36 
Cells,  17,  18 
Cerebellum,  anatomy,  130 

function,  130 

removal,  132 
Cerebral  vesicles,  198 
Cerebrum,  anatomy,  121-125 

fibres,  course  of,  125,  126 

functions,  127 
localization,  127 

unilateral  action,  127 

removal,  127 
Chorion.  190 

villi,  190 
Chyle,  55 

in  the  lacteals,  61 

quantity,  62 
Cliyme,  49 
Circulation  of  the  blood,  27 

apparatus,  27 

course,  28 
Color-blindness,  171 

209 


210 


INDEX. 


Connective  tissues,  19 
Corium,  70 
Corpora  striata,  126 

quadrigemiua,  120 
Corpus  luteum,  181,  182 
Corpuscles,  blood,  24 

varieties,  24-26 
Cranial  uerves,  auatomy,  13S-14o 

functions,  133-145 
Cream,  68 
Crura  cerebri,  auatomy,  120 

functions,  120 

D. 

Decidua  menstrualis,  181 

reflexa,  186 

vera,  186 
Defecation,  58 

Degeneration  of  a  nerve-fibre,  108 
Deglutitiou,  44,  46 
Development,  183-202 

alimeutarv  canal,  200 

brain,  197,  199 

cranial  uerves,  197 

cranium,  192 

ear,  200 

external  genitals,  202 
male,  202 
female,  202 

extremities,  193 

eye,  199 

face,  192 

heart,  194 

kidneys,  201 

lungs,"  201 

olfactory  apparatus,  200 

ovary,  202 

spinal  cord,  197 
nerves,  197 

testicle,  202 
Dialvsis,  59 
Diastole,  33 
Digestion,  42 

gastric,  50 
details  of,  50 

intestinal,  52 

nervous  mechanism,  51 
Diplopia,  171 
Ductus  arteriosus,  196 

venosus,  195 

E. 

Ear,  anatomy,  155-159 


Ear,  divisions,  155-159 

functions,  155-159 
Embrvo,  circulation,  193 
Embryology,  173-203 
Emmetropia,  1G6 
Endothelium,  18 
Energv,  91 
Epibla-st,  185-187 
Epidermis,  70 
Epithelium,  18 
Eustachian  valve,  196 
Exclusive  diet,  92 
Excretions,  64 
Eye,  anatomy,  162-165 

function,  160 
Eyelids,  161 

P. 

Fallopian  tubes,  177 

function,  177 
Foetal  circulation,  196 

changes  in,  after  birth,  197 
Fore-gut;  200 

G. 

Grastric  juice,  48 
secretion,  49 
function,  49 
Germinal  vesicle,  176 
Germinative  spot,  176 
Glosso-labio-laryngeal  paralysis,  119 
Graafian  follicles,  174 

H. 

Hearing,  155 

subjective  sensations,  160 
Heart,  28 

action,  32,  34 

auricles,  32 

cavities,  29 

foetal  circulation,  196 

force,  34 

nervous  influences,  35 

nourishment,  35 

sounds,  34 
cause,  34 

valves,  29 
function,  32,  33 

ventricles,  32 
action,  32 

work,  34 


INDEX. 


211 


Heat-centre,  64 
Hiud-jrut,  200 
Hypoblast,  1S5,  187 

I. 

Images,  169,  170 
Inhibition,  99,  112 
lusalivation,  43 
Iris,  165 
action,  165 

Kidneys,  anatomy,  73-75 
function,  74 

L. 

Lachrymal  gland,  161 
Large  intestine,  58 
Liver.  .55 

functions,  57,  53 
Lungs.  37 
Lymph.  62 

M. 

Mammary  glands.  67 
Mastication.  42.  43 

Medulla  oblongata,  anatomy,  113-116 
automatism.  117 
centres,  117.  113 
functions,  117-119 
Medullary  groove.  1S7 
Menstruation.  ISl 

character,  ISl 

duration,  181 
Mesoblast,  1S5,  187 
Metabolism,  63 
Micturition,  77 
Milk.  OS.  69 

sour.  6S 
Milk-curdling  ferments,  69 
Muller's  duct,  202 
Muscle.  82 

color,  84 

composition,  85 

contraction,  etc.,  S6-SS 

electrical  condition,  85 

fnnction,  &5 

varieties.  52,  83 
Muscles,  involuntary,  89 

voluntary,  89 


Myopia,  166 
Myosin,  83 


X. 


Nerves,  afferent.  i>> 

anatomy.  93,  94 

classification,  95,  97 

efferent,  96 

function,  95 

impulses,  97 
Xitrogenous  eqnilibriom,  91 
Normal  diet.  93 
Nutrition,  89 

o. 

Olfactory  nerves,  1-54 
Optic  nerve,  161 
function,  161 

thalami,  126 
ftinction,  126 

vesicle,  199 
Optograms.  169 
Ovaries,  173 
Over-feeding,  92 
Ovum,  176 

changes  after  impregnation,  183-185 

derivation,  175 

escape,  175 

impregnation,  179, 1^  183 

P. 

Paralysis,  varieties,  129 
Pancreas,  secretion.  53 
Parturition,  202,  203 
Penis.  IH) 
Pepsin.  49 
Peptone,  49.  50 
Personal  error.  97 

equation.  97 
Perspiration,  insensible,  70 
Placenta.  19*3.  191 
Placental  circulation,  195 
Pons  Varolii,  anatomy,  119 

functions.  120 
Primitive  groove.  185 
Presbyopia,  167 
Prostate  gland.  180 
Protoplasm.  17 
Protovertebne.  192 
Proximatf  principles,  19 

classification,  20^  21 


212 


INDEX. 


Ptyalin,  43 

starch,  44 
sugar,  44 
Pulse,  35 


K. 


Eefies  action,  98,  99,  112,  113 
Eeproduction,  173-183 
Eespiration,  36 

capacity,  38 

carbouic  acid,  39 

eiFect  on  tlie  blood,  40 
on  circulation,  42 

force,  38 

larynx,  39 

mechanism,  37 
nervous,  40 

modifications,  40 

nostrils,  39 

oxygen,  39 

rapidity,  38 

rhythm,  39 

vagus,  41 
Eetinal,  red,  169 
Eeturn  circulation,  36 
Eigor  mortis,  88,  89 
Eumination,  51 

S. 

Saliva,  43 

secretion,  44 
Saponification,  54 
Sebaceous  glands,  72,  73 
Secreting  glands,  65 

action,  66 
Secretions,  64 

correlation,  67 
Segmentation,  183,  184 
Sensation,  common,  146 

muscular,  149 

pressure,  149 

special,  146 

temperature,  149 
Seminal  vesicles,  180 
Sexual  generation,  173 
Sight,  160-172 
Skin,  69,  73 

Small  intestine,  anatomy,  52 
Smell,  153-155 
Species,  173 

Spermatic  fluid,  178,  179 
conveyance,  179 


Spermatic  fluid,  secretion,  178 
Spermatozoa,  179 

action,  179 
Sphygmograph,  35 
Spinal  cord,  anatomy,  104-106 
automatic  actions,  113 
course  of  fibres,  107,  108 

of  impulses,  109,  110 
division  of  lateral  half,  110 

of  nerve-roots,  107,  108 
function,  109 
reflex  actions,  112 
stimulation.  111 
Splanchuopleure,  187 
Spleen,  82 
Starvation,  92 
Stereoscope,  172 
Stomach,  46,  51 

glands,  47 
Strypsin,  54 
Sweat,  71 
amount,  72 
glands,  70 
ingredients,  72 
nervous  mechanism,  72 
Sympathetic  system,  99-104 
Systole,  33 


T. 


Taste,  150 

after,  153 
Teeth,  42 
Testicles,  178 
Tetaaus,  88 
Tongue,  150-153 
Touch,  147 

varieties,  147 

acuteness,  148 
Trypsin,  54 

u. 

Umbilical  cord,  191 

vesicle,  188 
Urea,  80,  81 
Urethra,  180 
Urine,  77 

abnormal  matters,  81 

acidity,  77 

composition,  78 

course,  77 

how  secreted,  76 

quantity,  79 


INDEX. 


213 


Urine,  secretion,  conditions  iifVcctinfr, 
7i) 

specific  gravity,  77 
Uterine  contractions,  203 
Uterns,  anatomy,  177 

changes  in  pregnancy,  186,  190 

V. 

Vagina,  anatomy,  178 
Vascular  glands,  81 
Vaso-motor  function,  103 
Veins,  30 

relative  area,  31 
Ventilation,  41,  42 
Vesicular  murmur,  38 


Villi,  r,n 

VKelline  circulation,  194 

nienii)rane,  176 
Vitellns,  176 
Voice,  160 
Vomiting,  51 

W. 

Wolffian  body,  201 
duct,  202 

Z. 

Zona  pellucida,  176 
cbanges,  185 


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